hey the ans is this 2s2 +4s4+6s6+8s8..............172s172+176s176+178s178+180s180

s2=s178=>the expression is 180(s2+s4+s6+..s88)+90s90+(180s180=0)

180(s2+s4+s6.......s90)-90s90

sina +s(a+d)+s(a+2d)+.............s(a+n-1)d)=s[n.diff/2]/s[diff/2]*s[a+L/2]

=>180[s45/s1*s46]
i think nw u can do it