Question

SinB=1/2 then 3cosB-4cos.cos.cosB

Answer 1

Since sinB=1/2, B=30°

substituting B

⇒ 3cos30°- 4COS³30°

⇒3 x √3/2 - 4 x (√3/2)³

⇒3√3/2 -3√3/2

⇒ 0

Answer 2

sinB=1/2
sin^2B+cos^2B=1
1/4+cos^2B=1
cosB=√3/2

therefore 3cosB-4cos^3B=3√3/2-4x3√3/8
=3√3/2-3√3/2
=0