Question

-cos10+ sin^210/2sin^25

Answer 1

$-cos10+\frac{sin^210}{2\, sin^25}=-cos10+\frac{(2sin5\cdot cos5)^2}{2\, sin^25}=-cos10+\frac{4\cdot sin^25\cdot cos^25}{2\, sin^25}=\\\\=-(cos^25-sin^25)+2cos^25=cos^25+sin^25=1$