Question

sin^2 5° + sin^2 10° +............+sin^2 180° =

Answer 1

sin^2 5+ sin^2 85 = 1
sin^2 10 + sin^2 80 = 1
sin^2 130 + sin^2 140 = 1
and 
sin^2 90 = 1
and
sin^2 45 + sin^2 135= 1
 adding all we get 18
∴18