sin\alpha*cos\alpha ?
sin\alpha + cos\alpha=\frac{3}{5}|()^2
(sin\alpha+cos\alph)^2=(\frac{3}{5})^2
sin^2\alpha+cos^2\alpha+2sin\alpha*cos\alpha=\frac{9}{25}
1+2sin\alpha*cos\alpha=\frac{9}{25}|-1
2sin\alpha*cos\alpha=\frac{9}{25}-\frac{25}{25}
2sin\alpha*cos\alpha=-\frac{16}{25}|:2
sin\alpha*cos\alpha=-\frac{16}{25}*\frac{1}{2}
sin\alpha*cos\alpha=-\frac{16}{50}