Question

The value of cos²20° + cos²70° is :
(1) O
(2) 1
(3) 1/2
(4) 1✓3​

Answer 1

Answer:

cos²20° + cos²70°

= cos²20° + cos²(90° – 20°)

= cos²20° + sin²20° = 1

[∵ cos (90° – θ) = sin θ]

1 is the correct answer