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Q5.    In a \Delta\textup{ABC}, \angle C = 3 \angle B = 2( \angle A + \angle B). Find the three angles.    

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Given,

\angle C = 3 \angle B = 2(\anlge A + \angle B)

\Rightarrow 3 \angle B = 2(\anlge A + \angle B)

\Rightarrow \angle B = 2 \angle A

\Rightarrow 2 \angle A -\angle B = 0..........(1)

 Also, As we know that the sum of angles of a triangle is 180, so

\angle A +\angle B+ \angle C=180

\angle A +\angle B+ 3\angle B=180^0

\angle A + 4\angle B=180^0..........(2)

Now From (1) we have 

\angle B = 2 \angle A.......(3)

Putting this value in (2) we have 

\angle A + 4(2\angle A)=180^0.

\Rightarrow 9\angle A=180^0.

\Rightarrow \angle A=20^0.

Putting this in (3)

\angle B = 2 (20)=40^0

And 

\angle C = 3 \angle B =3(40)=120^0

Hence three angles of triangles 20^0,40^0\:and\:120^0.

Posted by

Pankaj Sanodiya

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