1. ## sina*cosa=4/7 , a=?

sina*cosa=4/7 , a=?

2. $\sin{a} \cos{a} = \frac{4}{7}$

$2\sin{a} \cos{a} = 2 \cdot \frac{4}{7}$

$\sin(2a) = \frac{8}{7}$

there is no solution for "a" to satisfy this equation ... why?