Circle gets cozy in triangle

Geometry Level 3

In ABC \triangle{\text{ABC}} , AD \text{AD} , BD \text{BD} and CD \text{CD} are the bisectors of BAC \angle{\text{BAC}} , ABC \angle{\text{ABC}} and ACB \angle{\text{ACB}} respectively.
If AFDE \text{AFDE} is a rectangle such that AD = 10 cm \text{AD} = \text{10 cm} and AE = 8 cm \text{AE} = \text{8 cm} , find the area of the circle inscribed in ABC \triangle{\text{ABC}} .

Round your answer( in cm 2 {\text{cm}}^{2} ) to the nearest integer.


The answer is 113.

This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try refreshing the page, (b) enabling javascript if it is disabled on your browser and, finally, (c) loading the non-javascript version of this page . We're sorry about the hassle.

2 solutions

Ashish Menon
Jun 12, 2016

We know that incenter is the point of intersection of the angular bisectors. So, D \text{D} is the incenter of ABC \triangle{\text{ABC}} Now, since AFDE \text{AFDE} is a rectangle, AEB = 90 \angle{\text{AEB}} = {90}^{\circ} . So, DE \text{DE} is the inradius.

Using pythagoras' theorem:-
AD 2 = AE 2 + DE 2 DE = 10 2 8 2 DE = 36 DE = 6 \begin{aligned} {\text{AD}}^2 & = {\text{AE}}^2 + {\text{DE}}^2\\ \text{DE} & = \sqrt{{10}^2 - 8^2}\\ \text{DE} & = \sqrt{36}\\ \text{DE} & = 6 \end{aligned}

So, area of incircle = π r 2 = 22 7 × 6 2 = 113.142 113 cm 2 = \pi r^2\\ = \dfrac{22}{7} × 6^2\\ = 113.142\\ \approx \color{#69047E}{\boxed{113 {\text{cm}}^{2}}}

Nice one(+1)

Abhay Tiwari - 5 years ago

Log in to reply

Thanks! :)

Ashish Menon - 5 years ago

You copied my question, you posted a similar one ,how could you?

Rishabh Sood - 5 years ago

Log in to reply

Noo dude, i just copied the title. My question is totally different plz dont misunderstand me.

Ashish Menon - 5 years ago

Log in to reply

;-) knew you would get serious

Rishabh Sood - 5 years ago
Edwin Gray
Jul 7, 2018

Since the angle bisectors meet at pint D, then by definition, D is the inradius if the incircle. The line De is a radius and length of sqrt(100 - 64) by Pythagoras. Therefore the area is 36*pi , or approximately 113. Ed Gray

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...