Question

Prove that : 8 cos³20°-6 cos 20° = 1


Solve this problem quick. I will mark you brainleyst ​

Answer 1

Answer:

RULE :

cos3θ = 4 cos³θ - 3 cosθ

SOLUTION :

Now, 8 cos³20° - 6 cos20°

= 2 (4 cos³20° - 3 cos20°)

= 2 cos(3 × 20)°

= 2 cos60°

= 2 × 1/2

= 1