Question

cos square 5 + cos square 10 + cos square 15 + 1 + cos square 90 is equals to

Answer 1

I think this will help u

Answer 2

The correct question is To find the value of  cos²5 + cos²10 + ..... + cos²85 + cos²90.

ANSWER:

The value of cos²5+cos²10+ .....+cos²85+cos²90 is 17/2.

• We know that sin(90-θ) = cosθ.

• We have to find the value of cos²5+cos²10+cos²15+cos²20+...+cos²90

• Total number of terms = 18

• Now, we substitute cosθ = sin(90-θ).

• cos²5 + cos²10 + cos²15 + .... + cos²40 + cos²45 + sin²(90-50) + sin²(90-55) +....+ sin²(90-80)+ sin²(90-85)+ cos²90

= (cos²5+sin²5) + (cos²10+sin²10) + (cos²15+sin²15)+ .... (cos²40+sin²40) + cos²45+cos²90

= 8+1/2+0= 17/2