iran-konkur 2014 Q110

iran-konkur · Other · konkur-riazi_1393 Reciprocal Trig & Identities
110- What is $\cos\!\left(3\sin^{-1}\dfrac{2\sqrt{2}}{3}\right)$?
(1) $-\dfrac{23}{27}$ (2) $-\dfrac{19}{27}$ (3) $-\dfrac{5}{9}$ (4) $-\dfrac{4}{9}$
\textbf{110-} What is $\cos\!\left(3\sin^{-1}\dfrac{2\sqrt{2}}{3}\right)$?

\medskip
(1) $-\dfrac{23}{27}$ \hfill (2) $-\dfrac{19}{27}$ \hfill (3) $-\dfrac{5}{9}$ \hfill (4) $-\dfrac{4}{9}$

\medskip