tan20+4sin20=

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tan20+4sin20=
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tan20+4sin20=
tan20+4sin20=

tan20+4sin20=
tan20+4sin20
=(sin20+2sin40)/cos20
=(sin20+sin40+sin40)/cos20
=(2sin30cos10+sin40)/cos20
=(cos10+sin40)/cos20
=(sin80+sin40)/cos20
=2sin60cos20/cos20
=2sin60
=根号3

tan20+4sin20
=(sin20+4sin20cos20)/cos20
=(sin20+2sin40)/cos20
=(sin20+sin40+sin40)/cos20
=((sin30cos10-cos30sin10)+(sin30cos10+cos30sin10)+sin40)/cos20
=(2sin30cos10+sin40)/cos20

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tan20+4sin20
=(sin20+4sin20cos20)/cos20
=(sin20+2sin40)/cos20
=(sin20+sin40+sin40)/cos20
=((sin30cos10-cos30sin10)+(sin30cos10+cos30sin10)+sin40)/cos20
=(2sin30cos10+sin40)/cos20
=(cos10+sin40)/cos20
=(sin80+sin40)/cos20
=((sin60cos20+cos60sin20)+(sin60cos20-cos60sin20))/cos20
=2sin60cos20/cos20
=2sin60
=根号3
三角函数公式:
sinX+sinY=2sin((X+Y)/2)cos((X-Y)/2)
和差化积。

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