证明tan(90°-y)=(2cos^3y-cosy)/(siny-2sin^3y)
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证明tan(90°-y)=(2cos^3y-cosy)/(siny-2sin^3y)证明tan(90°-y)=(2cos^3y-cosy)/(siny-2sin^3y)证明tan(90°-y)=(2c
证明tan(90°-y)=(2cos^3y-cosy)/(siny-2sin^3y)
证明tan(90°-y)=(2cos^3y-cosy)/(siny-2sin^3y)
证明tan(90°-y)=(2cos^3y-cosy)/(siny-2sin^3y)
证明:∵tan(90°-y)=coty
=cosy/siny
=[cosy*cos(2y)]/[siny*cos(2y)]
=[cosy*(2cos²y-1)]/[siny*(1-2sin²y)] (应用余弦倍角公式)
=(2cos³y-cosy)/(siny-2sin³y)
∴原等式成立.
证明tan(90°-y)=(2cos^3y-cosy)/(siny-2sin^3y)
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