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sin20cos^2 25-sin20sin^2 25+cos^2 50+sin^2 20
=sin20(cos^2 25-sin^2 25)+cos^2 50+sin^2 20
=sin20cos50+cos^2 50+sin^2 20
=sin20sin40+sin^2 40+sin^2 20
=(sin20+sin40)^2-sin20sin40
=(2sin30cos10)^2-1/2[cos20-cos60]
=cos10^2-1/2(2cos10^2-1-1/2)
=3/4
=sin20(cos^2 25-sin^2 25)+cos^2 50+sin^2 20
=sin20cos50+cos^2 50+sin^2 20
=sin20sin40+sin^2 40+sin^2 20
=(sin20+sin40)^2-sin20sin40
=(2sin30cos10)^2-1/2[cos20-cos60]
=cos10^2-1/2(2cos10^2-1-1/2)
=3/4
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