Consider 
– (cos2 20° + cos2 70°)
= 
– (cos2 20° + cos2 (90° – 70°))
= (tan θ × cot θ) + (tan 50°/tan 50°) – (cos2 20° + sin2 20°)
= 1 + 1 – 1
= 1
AI is thinking…
Couldn't generate an explanation.
Generated by AI. May contain inaccuracies — always verify with your textbook.
