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求(sin40°+cos10°)/cos20° =(cos50°+cos10°)/cos20°

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求(sin40°+cos10°)/cos20° =(cos50°+cos10°)/cos20°
求(sin40°+cos10°)/cos20° =(cos50°+cos10°)/cos20°
(sin40°+cos10°)/cos20°
=【cos(π/2-40°)+cos10°】/cos20°
=(cos50°+cos10°)/cos20°
再问: 那(cos50°+cos10°)/cos20°=2cos30°cos20°/cos20°的过成了?
再答: ———— (cos50°+cos10°)=cos(30+20)+cos(30-20) ∴ cos50°+cos10°)/cos20° =【2cos(50+10)/2+cos(50-10)/2】/cos20 =2cos30°cos20°/cos20 【懒得打°了,希望不影响您=V=】