Q.

The angles of a triangle are in A.P. The number of degrees in the least is to be the number of radians in the greatest as 60:π. Then the greatest angle is

1 120°  
2 90°  
3 135°  
4 105°  

Ans.

(2)

Let the angles of the triangle be  (a-d)°,  a°,  (a+d)°

Their sum is a-d+a+a+d=180

⇒3a=180⇒a=60

Again, by the given condition,

a-d(a+d)π180=60π⇒3(a-d)a+d=1

⇒3a-3d=a+d

⇒2a=4d            ⇒   a=2d

∴  60=2d           ∴    d=30

Hence, the greatest angle =60+30=90°