$16cos^3\frac{\pi}{6}-12cos\frac{\pi}{6}=$ _____.
Answer & explanation
Correct answer: option 1
16cos3\(\frac{π}{6}\) - 12 cos \(\frac{π}{6}\)
Using formula ,
4cos3A - 3 cosA = cos3A
= 4 ( 4 cos3\(\frac{π}{6}\) - 3 cos \(\frac{π}{6}\) )
= 4 ( cos 3 × \(\frac{π}{6}\) )
= 4 × cos\(\frac{π}{2}\)
= 0