Question

(G1 - ifce 2014) Se sen(x) = -2/3, cos(2x) x sen(-x) é:a) 2/9b)2/27c)-2/9d)-2/27e)-9/27

Answer 1

$\cos{2x}\cdot\sin{(-x)}$

$(\cos^2{x}-\sin^2{x})\cdot-\sin{x}$

$(1-2\sin^2{x})\cdot-\sin{x}$

$[1-2\cdot(-\frac{2}{3})^2]\cdot\frac{2}{3}$

$(1-\frac{8}{9})\cdot\frac{2}{3}$

$\frac{1}{9}\cdot\frac{2}{3}$

$\boxed{\frac{2}{27}}$

Alternativa B.