cos-2-3-sin-pi-2-3sin-2-7pi-2-2cos-5pi-

Question Number 164757 by mathlove last updated on 21/Jan/22

\cos α = \frac{2}{3}

s i n (\frac{π}{2} + α) - 3 {s i n}^{2} (\frac{7 π}{2} + α) - 2 c o s (5 π + α) = ?

Commented by blackmamba last updated on 21/Jan/22

\Rightarrow= \cos α - 3 \cos^{2} α + 2 \cos α

\Rightarrow= 3 \times \frac{2}{3} - 3 \times \frac{4}{9}

\Rightarrow= \frac{6 - 4}{3} = \frac{2}{3}