Question

if sinB=1/2, show that 3cosB-4cos^3B=0

Answer 1

Given, sinB=1/2

  (or)  sinB=30° 

Now 3cosB-4cos3B= 3(cos30)-4(cos330)

  =3×(√3/2)-4× (√3/2)3  

   = (3√3/2)-4(3√3/8)

                                  =  3√3/2 - 3√3/2 =0