作业帮tan20度+4sin20度=?如题
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tan20度+4sin20度=?如题
tan20度+4sin20度=?
如题
tan20度+4sin20度=?如题
tan20度+4sin20度
=(sin20+4sin20cos20)/cos20
=(sin20+2sin(60-20))/cos20
=根号3*cos20/cos20
=根号3
tan20+4sin20
=sin20/cos20+4sin20
=(sin20+4sin20cos20)/cos20
=(sin20+2sin40)/cos20
=(sin20+sin40+sin40)/cos20
=(2sin30cos10+sin40)/cos20
=(cos10+sin40)/cos20
=(sin80+sin40)/cos20
=2sin60cos20/cos20
=2sin60
=根号3
原式=sin20/cos20+4sin20
=(sin20+4sin20*cos20)/cos20
=(sin20+2sin40)/cos20
=[sin(60-40)+2sin40]/cos(60-40)
=(sin60cos40-cos60sin40+2sin40)/(cos60cos40+sin60sin40)
...
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原式=sin20/cos20+4sin20
=(sin20+4sin20*cos20)/cos20
=(sin20+2sin40)/cos20
=[sin(60-40)+2sin40]/cos(60-40)
=(sin60cos40-cos60sin40+2sin40)/(cos60cos40+sin60sin40)
=[(根号3)/2*cos40-1/2sin40+2sin40]/[1/2cos40+(根号3)/2sin40]
=根号3
关键是最后一部，上下差一个根号3
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