3sin 2 20 0 -2tan 2 45 0 +3sin 2 70 0 =?
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3sin²20°-2tan²45°+3sin²70°
=3sin²20°-2(1)²+3sin²(90°-20°)
=3sin²20°-2+3cos²20°
=3(sin²20°+cos²20°)-2
=3-2
=1
=3sin²20°-2(1)²+3sin²(90°-20°)
=3sin²20°-2+3cos²20°
=3(sin²20°+cos²20°)-2
=3-2
=1
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