Cos2 10-cos10 cos50+cos2 50
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3/4
Step-by-step explanation:
= cos²10 + cos²50 - cos10 cos50
= 1/2 (1 + cos20 + 1 + cos100 - cos60 - cos40)
= 1/2 (3/2 + 2 cos60 cos40 - cos40)
= 1/2 × 3/2
= 3/4
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