问题
解答题
已知tanα=2,试求值; (1)
(2)sin2α-sinα•cosα-2cos2α |
答案
(1)
=2sin(π-α)-cos(α+
)π 2 cos(α-π)+sin(α-
)π 2
=-2sinα+sinα -cosα-cosα
,tanα=-33 2
(2)sin2α-sinα•cosα-2cos2α=
=sin 2α-sinα•cosα-2cos 2α sin2α+cos2α
=0tan2α-tanα-2 tan2α+1