Question

10*sin40*sin50/cos10

Answer 1

$frac{10sin40sin50}{cos10} = frac{10(cos(40-50)-cos(40+50))}{2cos10} = \ =frac{5(cos(-10)-cos90)}{cos10} =frac{5(cos10-0)}{cos10} =frac{5cos10}{cos10} =5$

Answer 2

$frac{10sin40*sin50}{cos10}= frac{10sin40*sin(90-40)}{cos10}= frac{10sin40*cos40}{cos10}=$
$= frac{5sin80}{cos10}= frac{5sin(90-10)}{cos10}= frac{5cos10}{cos10}=5$