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数学
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sin(π/4-x)=5/13,则sin2x=?
人气:471 ℃ 时间:2020-01-29 17:23:31
解答
sin2x
=cos(π/2-2x)
=cos2(π/4-x)
=1-2[sin(π/4-x)]^2 (余弦2倍角公式)
=1-2(5/13)^2
=119/169.
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