How three medians conference at centroid divides triangle area right into 3 and also 6 equal parts and also properties that cevians

Centroid divides triangle area right into 3 equal parts created by the longer median segments at centroid and 6 equal parts by all six average segments in ~ centroid.

You are watching: Divide a triangle into 3 equal parts

Also a allude on a cevian divides a triangle area in the ratio of its segment at the point.

Medians conference at centroid create a rich collection of relations involving fragmentized areas and segmented lines consisting of the political parties of the triangle.

Contents are,

How each average divides triangle area into two equal parts.Relation between locations of the triangles developed by the medians at centroid and a line parallel come a base and passing with the mid-points that the various other two sides.Area to cevian segment proportion concept: A triangle area is split in the same proportion as the cevian segment proportion at a point that acts together the peak of a 2nd triangle.Area the triangle native length the medians.

A typical divides a triangle into 2 parts of same area

In the adhering to figure, ad is a median of $ riangle ABC$ bisecting the opposite side BC in ~ D. The centroid is the point G through which the various other two medians, if drawn, would pass. AH is the altitude that the triangle with BC together the base; and also PAQ is a heat parallel to base BC.


With basic BC and altitude AH the area that $ riangle ABC$ is,

$A=frac12BC imesAH$.

AS $BD=CD=frac12BC$, area of $ riangle ABD$ is,

$A_ABD=frac12BD imesAH=frac14BC imesAH=frac12A$.

For $ riangle ADC$ additionally altitude is exact same AH, like any triangle with base BC and also vertex lied on heat PAQ parallel come it. Therefore area that $ riangle ADC$ is,

$A_ADC=frac12DC imesAH=frac14BC imesAH=frac12A$.

Thus the median advertisement divides the area that the triangle into two equal parts.

Before us next show you how three medians division the area that a triangle right into six equal parts, we will generalize the very first result into the an effective concept of Area to base department ratio, and also show that is mechanism.

Area to base department ratio concept

The following figure represents the difficulty solution.


In $ riangle ABC$, together line segment ad from peak A to base BC divides BC in the ratio of, $CD:BD=x:y$, the proportion of areas of $ riangle ACD$ and $ riangle ABD$ will likewise be $x:y$. Come formally state this essential general result,

A heat segment indigenous a peak of a triangle come the the contrary side, i m sorry is the base, divides the base and also the triangle area in the exact same ratio.

Proof the area to base division ratio concept

In $ riangle ABC$, line segment ad divides the base BC in ~ D for this reason that,


As both the triangles, $ riangle ACD$ and $ riangle ABD$ have actually same altitude AP i m sorry is additionally the altitude of parental $ riangle ABC$,

$ extArea of riangle ABD=A_ABD=frac12BD imesAP$.


$ extArea of riangle ACD=A_ACD=frac12CD imesAP$.

Taking the proportion of the latter to the former,


The an outcome is really an easy but general.

A special case is when advertisement is the median and $CD=BD$. In this situation then, the typical divides the triangle right into two components of same areas.

As another example, if $BD=2CD$,


We will usage this last result to explain how the 3 medians divide a triangle into six regions of same area.

All three medians together divide a triangle right into 6 equal parts, proof

The following number will help explain the system of this relationship. AD, BE and also CF space the 3 medians splitting the $ riangle ABC$ into six part triangles meeting suggest of which is the centroid G. AP is the perpendicular to typical BE and is the altitude that all three triangles $ riangle ABG$, $ riangle AEG$ and $ riangle ABE$.


The medians division the triangle into six non-overlapping triangular areas with vertices conference at centroid G. These six triangles in reality consist of three pairs of equal triangles formed by the division of three triangles created from the centroid and three pairs of vertices, through the part of mean from vertex G come the base. For example, areas of one such same area pair that triangles host the relation,


Our target is to present area of one nearby pair of the 3 pairs of triangles as equal. For example we will show,


$ riangle ABE$ is separated into 2 triangles $ riangle ABG$ and also $ riangle AEG$ through the mean section $AG$ event on basic BE at G.

As be is a median, by the median section proportion at centroid concept, it is separated into two sections BG and also EG with a ratio, $BG:EG=2:1$ .

So by the area to base department ratio concept,


Again, in $ riangle ABG$,



$A_AEG=A_AFG$, that is, a pair of surrounding triangles space equal in area.

This makes locations of all six triangles v coincident vertices at G equal.

Three vertex come centroid line segments divide a triangle right into 3 same parts

By this concept, G gift the centroid, in figure below GA, GB and also GC division the triangle right into 3 same parts.


This can conveniently be break up by adding up adjacent equal pairs of six equal triangles produced by the 3 medians together in the ahead section.

Before we proceed to the next sections we need to explain the often used Triangle similarity rich concept.

Triangle similarity wealthy concept, the mechanism

The following number will aid explanation the the concept.


We official state the triangle similarity affluent concept as,

Ratio of all pairs of corresponding sides of equivalent pairs that triangles formed by a straight line parallel to the base will be equal.

Alternatively this result leads to,

A directly line parallel to the basic of a triangle will divide all straight line part dropped native the vertex to the basic in same ratio.

This an effective rich principle is used generally in both forms.

To be specific, through respect come the figure above, the line $PQ||BC$, the base, cuts throughout four lines $AB$, $AM$, $AN$ and $AC$ dropped indigenous vertext A to the basic BC at the points D, E, F and also G respectively in equal ratio. The is come say,


This is the second type of the wealthy concept and also it follows from the more comprehensive first form of the an interpretation of the concept.

Primary form of the triangle similarity wealthy concept

The line PQ||BC forms six bag of corresponding triangles through cutting across the four lines dropped indigenous the vertex to the base,

$ riangle ADE$ and $ riangle ABM$,

$ riangle AEF$ and also $ riangle AMN$,

$ riangle AFG$ and also $ riangle ANC$,

$ riangle ADF$ and $ riangle ABN$,

$ riangle AEG$ and also $ riangle AMC$, and also finally,

$ riangle ADG$ and $ riangle ABC$.

In each together pair the triangles, the ratio of the equivalent sides will be equal, therefore that ratio of all pairs of matching sides will be equal.

This amounts partially to,


There will certainly be much more such same ratios.

This happens mostly because, say in the pair of triangles, $ riangle ADG$ and also $ riangle ABC$,

the edge at the crest $angle A$ is common, andthe remainder of the 2 pairs of angles, $angle ADG=angle ABC$, and $angle AGD =angle ACB$, together each of ab and AC intersects a pair of parallel present DG and BC.

The three pairs of matching angles gift equal, the $ riangle ADG$ and also $ riangle ABC$ are similar so that proportion of all 3 pairs of matching sides come to be equal.

The same mechanism works in every pair of matching triangles.

It is trivial to display that this result leads come the second kind of definition of this necessary rich concept.

We require to explain one an ext rich concept, the area come cevian segment ratio, prior to taking increase the following sections.

A cevian is,

A line from a vertex getting to or cross the opposite side of a triangle.

Area come cevian segment ratio concept, proof

The following number will help the definition and proof of concept.


A cevian is defined as,

A line from a vertex reaching or cross the opposite next of a triangle.

In figure over AD is together a cevian. Special situations of cevians are, the median and also the altitude the the triangle.

Area come cevian segment ratio concept formally states,

Any allude on a cevian dividing the line into a ratio of $x:y$ will likewise divide the whole area the the triangle right into two areas in the same proportion by acting together the crest of 2nd triangle inside the key triangle.


Ratio the the 2 line part made by a suggest on a cevian will certainly be very same as the proportion of the two locations formed by the point as a peak of a triangle with base very same as the original triangle.

Specifically through respect to the figure,

$AF:FD= extArea of region ABFCA: extArea of riangle BFC$.

Here suggest F divides the cevian advertisement into two sections FD and also AF at a proportion of $x:y$.

It follows from this result,


We get this result just by fraction inversion, enhancement of 1 and also then turning back back.

Let united state see why this principle works.

In $ riangle ABD$ with advertisement as base, applying area to base division ratio concept,


Similarly in $ riangle ACD$ with ad as base, and applying the same ide we get,


So by proportion concepts,


Or, $A_BFC:A_ABC=x:(x+y)$.

Special case of centroid together the cevian point on a median, the cevian in this case

As a special case, if F is the centroid, ad is a typical so that F divides the median in a ratio,

$FD:AF=1:2$, and so in this distinct case,


In other words, the area that the $ riangle BFC$ will be one-third the the main $ riangle ABC$.

With these rich concepts in place we are now ready to go ahead in taking care of the rest of the principles elegantly.

Additional helpful relations in between the locations of the triangles developed by the medians at the centroid

We will use the following figure to describe the concept in this section. Specifically we will certainly see how the area that the triangle $ riangle GFP$, $ riangle GEP$ or $ riangle BGC$ are regarded each other and to the area that the key $ riangle ABC$.


In this ar we will discover what space the ratios of the locations of the triangles, $ riangle GFP$, $ riangle GFE$ and $ riangle BGC$ with respect come the area of the parental triangle.

Area of $ riangle GFP$ v respec come area the $ riangle GFE$

As median ad is the line from vertex to the critical triangle base BC, passing v the bases the triangles, $ riangle AFE$ and $ riangle AGE$, where these two have actually a usual base FE, the median ad bisects FE additionally at P. We conclude this result by applying the Triangle similarity affluent concept.



Thus GP divides the $ riangle GFE$ in two equal parts. We conclude this native the ide of a median bisecting the area the a triangle.

This result says then,


Area the $ riangle GFE$ v respect to area of $ riangle ABC$

To resolve this difficulty we will identify the level of GP.

By triangle similarity rich concept,


Adding PG to the equation,


Again by median section proportion at centroid concept,



$DG=2PG$, which we suspected to be true, yet now we know.

As $DG=frac13AD$,

$PG=frac16AD$, wherein $AD$ is the median.

Flipping $ riangle GFP$ vertically through its vertex relocated along the median

When we execute this, we kind the rectangle GEHF through its diagonals bisected in ~ P, and also its area bisected by typical base FE.



By area come cevian segment proportion concept then,



$A_AFE=frac14A_ABC$, as both base and also altitude that the smaller sized triangle are half of those that the larger triangle.

Relating the areas of all these triangles,


The last an outcome we gain fro one earlier an outcome of,

$A_BGC=frac13A_ABC$, together GD is one-third the AD.

Note that we have not offered the altitude or the basic lengths. We can avoid this since of symmetric relationship in between the median and the bases and also hence the locations through the use of the powerful rich concepts.

Area that triangle indigenous lengths that its medians, proof

The figure below will assist the explanation.


As usual, AD, BE and CF room the 3 medians the $ riangle ABC$ intersecting in ~ centroid G.

The values, $AD=m_1$, $BE=m_2$ and $CF=m_3$ space given. We are to derive the area of the $ riangle ABC$.

As us know, offered three political parties of a triangle together a, b and also c, its semi-perimeter,

$s=frac12(a+b+c)$, and the area,


We require then to construct a triangle with 3 sides as the medians, derive relation between the area the triangle the medians to the area that the original triangle and also then gain the area the the initial triangle by deriving area of triangle the medians by utilizing semi-perimeter concept.

Construction that triangle that medians

To construct the triangle of medians, first we have actually kept the side of median ad fixed, and translated the side of median BE in direction parallel to BC through the street BD to reach the place DQ. This parallel translation has resulted in, $BE||DQ$ and also $BE=DQ$ as well as, $EQ||BD||BC$ and also $EQ=BD=DC$. This has created the second side of the triangle the medians.

To kind the third side, the third median CF has actually been analyzed in direction parallel to ab to AQ, for this reason that, $CF||AQ$ and $CF=AQ$ as well as, $CQ||AF||AB||DE$ and $CQ=AF=FB=DE$.

In resulting parallelogram DEQC, the 2 diagonals bisect every other, for this reason that, $ER=CR$ and $DR=QR$, so the AR is the median that $ riangle ADQ$ that is made up of medians ot the original $ riangle ABC$.

Thus AR divides the area the $ riangle ADQ$ into two equal parts each that which, say, is $x$.

AS $AE=EC=2ER$, $AR=AE+ER=3ER$, that is,

$ER=frac13AR$, giving

$A_DER=A_DCR=frac13A_ADR=z$, say.

Now we will use the following number simplified from the over figure to placed forth the last piece the reasoning.


We have actually removed the medians BE and also CF as a cleanup measure.

Let united state denote,

Area of $ riangle ABD=A_ABD=y$,

Area the $ riangle ADR=A_ADR=x$, and

Area of $ riangle DCR=A_DCR=z$.

And area of $ riangle ABC$ is, $A_ABC=2y$, and area that $ riangle ADQ$ is, $A_ADQ=A_m=2x$.





In various other words, the area of any type of triangle is four-thirds the the area of the triangle formed from the medians.

As we know exactly how to find the area of a triangle from its provided side lengths, the is a an easy step an ext to find the area that the $ riangle ABC$ native the provided length of its medians.

Lastly us will simply skim v the concern of finding the area of an it is intended triangle in terms of its sides or medians.

Area of an it is provided triangle from its sides and medians

The following figure will aid the explanation.


As median ad of it is provided $ riangle ABC$ of side length $a$ is perpendicular to opposite side BC bisecting it, the area that the triangle is,

$A_ABC=frac12BC imesAD$.

By the usage of Pythagorean theorem we have,

$AD=m=sqrta^2-left(fraca2 ight)^2=sqrtfrac34a^2=fracsqrt32a$.


$A_ABC=fracsqrt34a^2=frac1sqrt3m^2$, wherein $a$ is the side size of the it is intended $ riangle ABC$ and $m$ is the size of all its 3 medians.

Note: Being customers of expertise for solving troubles the best way possible, we need to understand the mechanism behind a principle in together clear terms as possible. The clarity of expertise of a principle goes a long means in enhancing our belief on the concept and also consequently our ability to use the principle when the is yes, really needed.

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