Question

sendo cos x= 1/4 e 3pi/2 < x < 2pi, calcule sen 2x e cos 2x

Answer 1

Como sen 2x = 2 sen x cos x e sen^2 x cos^2 x=1, temos que:

(1/4)^2 + cos^2 x = 1
cos^2 x = 1- 1/16
cos x =  \sqrt{15/16}
cox x = sqtr{15}/4

Daí temos que Sen 2x = 2 * 1/4 * \sqtr{15}/4 = \sqtr{15}/8$sqtr{15}/4$$\sqrt{15}/4$