求tan20°+4sin20°的值．
问题描述：
求tan20°+4sin20°的值．
答
tan20°+4sin20°=
sin20°+4sin20°cos20° cos20°
=
sin20°+2sin40° cos20°
=
(sin20°+sin40°)+sin40° cos20°
=
2sin30°cos10°+sin40° cos20°
=
=sin80°+sin40° cos20°
2sin60°cos20° cos20°
=2sin60°=
．
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