问题
解答题
求tan20°+4sin20°的值．
答案
tan20°+4sin20°=sin20°+4sin20°cos20° cos20°
=sin20°+2sin40° cos20°
=(sin20°+sin40°)+sin40° cos20°
=2sin30°cos10°+sin40° cos20°
=
=sin80°+sin40° cos20° 2sin60°cos20° cos20°
=2sin60°=
．3
