`sin^(2)5^(@)+sin^(2)10^(@)+sin^(2)15^(@)+ . . . .+sin^(2)85^(@)+sin^(2)90^(@)` is equal to

Options

A. `7(1)/(2)`
B. `8(1)/(2)`
C. `9`
D. `9(1)/(2)`

Answer

d

Explanation

`(sin^(2)5^(@)+sin^(2)10^(@)+..........+sin^(2)85^(@))+sin^(2)90^(@)`
No. of term`={((85-5)/(5))+1}+1`
`=(17)/(2)+1`
sum of seris `=9(1)/(2)`
[use this approach in eaxm]