Question

Cos 5° + Cos 10° + Cos 15° + Cos 20° + upto Cos 180° =​

Answer 1

Answer:

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

Answer 2

Step-by-step explanation:

Answer in the figure

Hope this will help you