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原式=lim<x~1>tan(πx/2)/[1/(1-x)]
=lim<x~1>[sec²(πx/2)×(π/2)]/[1/(1-x)²]
=(π/2)*lim<x~1>(1-x)²/cos²(πx/2)
=(π/2)*lim<x~1>[2(x-1)]/[2cos(πx/2)*(-sin(πx/2)*(π/2)]
=lim<x~1>(x-1)/[(-1/2)sin(πx)]
=-2*lim<x~1>(x-1)/sin(πx)
=-2*lim<x~1>1/[π*cos(πx)]
=-2×(-1/π)
=2/π
=lim<x~1>[sec²(πx/2)×(π/2)]/[1/(1-x)²]
=(π/2)*lim<x~1>(1-x)²/cos²(πx/2)
=(π/2)*lim<x~1>[2(x-1)]/[2cos(πx/2)*(-sin(πx/2)*(π/2)]
=lim<x~1>(x-1)/[(-1/2)sin(πx)]
=-2*lim<x~1>(x-1)/sin(πx)
=-2*lim<x~1>1/[π*cos(πx)]
=-2×(-1/π)
=2/π
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谢谢了
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