Question

TR16 NOMETRY.-
AssiGNMENT - 3.
بي
If sin B = 1/2show that3 cosB-4coscubeB=0​

Answer 1

sinB = 1/2 => B = 30⁰

We know, 3cosB-4cos³B = cos3B (It's a formula, don't ask me how XD)

cos3B = cos(3*30⁰) = cos(90⁰) = 0

If you don't want to use the formula,

sin²B + cos²B = 1 => cosB = √(1-sin²B)

=> cosB = √3/2

3cosB-4cos³B = (3√3)/2 - 4*(3√3/2)³

=>3cosB-4cos³B = 0

Hope this helps...