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(sin20*sin10)/(cos20*cos10)
人气:364 ℃ 时间:2019-12-12 07:13:54
解答
sin20=2sin10cos10
cos20=1-2(sin10)^2
原式=2(sin10)^2/[1-2(sin10)^2]
=-1+1/[1-2(sin10)^2]
=-1+1/cos20
=sec20-1
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