נושא : שימוש בזהויות s i n 3 α + s i n α ∗ c o s 2 α = s i n α ? s i n α ( s i n 2 α + c o s 2 α ) = s i n α c o s 2 α + s i n 2 α = 1 s i n α = s i n α {\displaystyle {\begin{aligned}&sin^{3}\alpha +sin\alpha *cos^{2}\alpha =sin\alpha ?\\&sin\alpha (sin^{2}\alpha +cos^{2}\alpha )=sin\alpha \\&\color {blue}cos^{2}\alpha +sin^{2}\alpha =1\\&sin\alpha =sin\alpha \\\end{aligned}}}
