证明(1+sinx)/cosx =(tanx+secx-1)/(tanx-secx+1)

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证明(1+sinx)/cosx =(tanx+secx-1)/(tanx-secx+1)
证明(1+sinx)/cosx =(tanx+secx-1)/(tanx-secx+1)

证明(1+sinx)/cosx =(tanx+secx-1)/(tanx-secx+1)
右边=(sinx/cosx+1/cosx-1)/(sinx/cosx-1/cosx+1)
上下乘cosx
=(sinx+1-cosx)/(sinx-1+cosx)
=(sinx+1-cosx)²/[sin²x-(1-cosx)²]
=(sin²x+cos²x+1-2sinxcosx+2sinx-2cosx)/(sin²x-1+2cosx-cos²x)
=(1+1-2sinxcosx+2sinx-2cosx)/(1-cos²x-1+2cosx-cos²x)
=-2(sinxcosx-sinx+cosx-1)/(2cosx-2cos²x)
=-2(sinx+1)(cosx-1)/[2cosx(1-cosx)]
=(sinx+1)/cosx
=左边
命题得证

原式=3X²-2X²+XY-2Y²+Y²+XY-X²
=2XY-Y²
=2×0.1×(-0.5)²-(-0.5)²
=-0.2 原式=3X²-2X²+XY-2Y²+Y²+XY-X²
=2XY-Y²
=2×0.1×(-0....

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原式=3X²-2X²+XY-2Y²+Y²+XY-X²
=2XY-Y²
=2×0.1×(-0.5)²-(-0.5)²
=-0.2 原式=3X²-2X²+XY-2Y²+Y²+XY-X²
=2XY-Y²
=2×0.1×(-0.5)²-(-0.5)²
=-0.2 原式=3X²-2X²+XY-2Y²+Y²+XY-X²
=2XY-Y²
=2×0.1×(-0.5)²-(-0.5)²
=-0.2

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