求值cos20°(1-根号3*tan50°)

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求值cos20°(1-根号3*tan50°)
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求值cos20°(1-根号3*tan50°)
求值cos20°(1-根号3*tan50°)

求值cos20°(1-根号3*tan50°)
cos(20°)〔1-√3 tan(50°)〕
=cos(20°)〔1-√3 sin(50°)/cos50°〕
=2[cos20/cos50] *[(1/2)sin50-(√3/2 )sin50]
=2[cos20/cos50] *[sin30 sin50-cos30sin50]
=2[cos20/cos50] *[sin-20 ]
=-2sin20cos20/cos50
= - sin40/cos50
=-cos50/cos50
=-1