Question

Решить...........................

Answer 1

Ответ: sin2α=-0,96.

Объяснение:

$sin\alpha =\frac{4}{5}=0,8\ \ \ \ \ \ \alpha \in(\frac{\pi }{2} ;\pi )\ \ \ \ \ \ sin2\alpha =?\\\\sin^2\alpha +cos^2\alpha =1\ \ \ \ \Rightarrow\\\\cos^2\alpha =1-sin^2\alpha =1-(0,8)^2=1-0,64=0,36.\\\\cos\alpha =б\sqrt{0,36}=б0,6.\ \ \ \ \ \ \alpha \in(\frac{\pi }{2} ;\pi )\ \ \ \ \Rightarrow\\\\ cos\alpha =-0,6.\\\\sin2\alpha =2*sin\alpha *cos\alpha=2*0,8*(-0,6 )=-0,96.\\\\sin2\alpha =-0,96.$