求tan70°+tan20°等于多少?
tan70°+tan20°
=sin70°/cos70°+sin20°/cos20°
=(sin70°cos20°+sin20°cos70°)/(cos70°cos20°)
=sin90°/{[cos(70°+20°)+cos(70°-20°)]/2}
=2/(cos90°+cos50°)
=2/cos50°
≈3.1114
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tan70°+tan20°
=sin70°/cos70°+sin20°/cos20°
=(sin70°cos20°+sin20°cos70°)/(cos70°cos20°)
=sin90°/{[cos(70°+20°)+cos(70°-20°)]/2}
=2/(cos90°+cos50°)
=2/cos50°
≈3.1114