1/sin(10)-√3/sin(80)的值是 - 知识问答

1/sin(10)-√3/sin(80)的值是

2个回答

=1/sin10-√3/cos10
=(cos10-√3sin10)/(sin10cos10)
=2*(1/2cos10-√3/2sin10)/(sin10cos10)
=2*(sin30cos10-cos30sin10)/(sin10cos10)
=4(sin(30-10))/(2sin10cos10)
=4(sin20)/sin20
=4
用到公式 sinacosb-sinbcosa=sin(a-b) sin2a=2sinacosa

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