Question

Найдите sina, если cosa=0,7 и 0 градусов < a < 90 градусов

Answer 1

$cos \alpha =0,7\\\\sin^2 \alpha +cos^2 \alpha =1\; \; \Rightarrow \; \; sin \alpha =\pm \sqrt{1-cos^2 \alpha }\\\\0\ \textless \ \alpha \ \textless \ 90\; \; \to \; \; sin \alpha \ \textgreater \ 0\\\\sin \alpha =+\sqrt{1-0,7^2}=\sqrt{0,51}$