A triangle has vertices A, B, and C. Vertex A has an angle of $\frac{π}{2}$ $pi/2$ , vertex B has an angle of $\frac{π}{4}$ $( pi)/4$ , and the triangle's area is $28$ $28$ . What is the area of the triangle's incircle?

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A triangle has vertices A, B, and C. Vertex A has an angle of $\frac{π}{2}$ $pi/2$ , vertex B has an angle of $\frac{π}{4}$ $( pi)/4$ , and the triangle's area is $28$ $28$ . What is the area of the triangle's incircle?

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Answer 1 · 2017-07-05T07:52:45

The area of the incircle is $= 15.1 u^{2}$ $=15.1u^2$

Explanation:

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The area of the triangle is $A = 28$ $A=28$

The angle $ˆ A = \frac{1}{2} π$ $hatA=1/2pi$

The angle $ˆ B = \frac{1}{4} π$ $hatB=1/4pi$

The angle $ˆ C = π - (\frac{1}{2} π + \frac{1}{4} π) = \frac{1}{4} π$ $hatC=pi-(1/2pi+1/4pi)=1/4pi$

The sine rule is

$\frac{a}{sin ˆ A} = \frac{b}{sin ˆ B} = \frac{c}{sin ˆ C} = k$ $a/(sin hat (A))=b/sin hat (B)=c/sin hat (C)=k$

So,

$a = k sin ˆ A$ $a=ksin hatA$

$b = k sin ˆ B$ $b=ksin hatB$

$c = k sin ˆ C$ $c=ksin hatC$

Let the height of the triangle be $= h$ $=h$ from the vertex $A$ $A$ to the opposite side $B C$ $BC$

The area of the triangle is

$A = \frac{1}{2} a \cdot h$ $A=1/2a*h$

But,

$h = c sin ˆ B$ $h=csin hatB$

So,

$A = \frac{1}{2} k sin ˆ A \cdot c sin ˆ B = \frac{1}{2} k sin ˆ A \cdot k sin ˆ C \cdot sin ˆ B$ $A=1/2ksin hatA*csin hatB=1/2ksin hatA*ksin hatC*sin hatB$

$A = \frac{1}{2} k^{2} \cdot sin A \cdot sin B \cdot sin C$ $A=1/2k^2*sinA*sinB*sinC$

$k^{2} = \frac{2 A}{sin A \cdot sin B \cdot sin C}$ $k^2=(2A)/(sinA*sinB*sinC)$

$k = \sqrt{\frac{2 A}{sin A \cdot sin B \cdot sin C}}$ $k=sqrt((2A)/(sinA*sinB*sinC))$

$= \sqrt{\frac{56}{sin (\frac{1}{2} π) \cdot sin (\frac{1}{4} π) \cdot sin (\frac{1}{4} π)}}$ $=sqrt(56/(sin(1/2pi)*sin(1/4pi)*sin(1/4pi)))$

$= 10.58$ $=10.58$

Therefore,

$a = 10.58 sin (\frac{1}{2} π) = 10.58$ $a=10.58sin(1/2pi)=10.58$

$b = 10.58 sin (\frac{1}{4} π) = 7.48$ $b=10.58sin(1/4pi)=7.48$

$c = 10.58 sin (\frac{1}{4} π) = 7.48$ $c=10.58sin(1/4pi)=7.48$

The radius of the incircle is $= r$ $=r$

$\frac{1}{2} \cdot r \cdot (a + b + c) = A$ $1/2*r*(a+b+c)=A$

$r = \frac{2 A}{a + b + c}$ $r=(2A)/(a+b+c)$

$= \frac{56}{25.55} = 2.19$ $=56/(25.55)=2.19$

The area of the incircle is

$a r e a = π \cdot r^{2} = π \cdot {2.19}^{2} = 15.1 u^{2}$ $area=pi*r^2=pi*2.19^2=15.1u^2$

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A triangle has vertices A, B, and C. Vertex A has an angle of $\frac{π}{2}$ $pi/2$ , vertex B has an angle of $\frac{π}{4}$ $( pi)/4$ , and the triangle's area is $28$ $28$ . What is the area of the triangle's incircle?

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