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∫(lntAnx/sin2x)Dx

∫(lntanx/sin2x)dx =∫(lntanx)/2sinxcosx)dx =½∫(lntanx)cosx/(sinxcos²x)dx =½∫(lntanx)cosx/(sinx)dtanx =½∫(lntanx)/tanx)dtanx =½∫(lntanx)d(lntanx) =¼ [ln(tanx)]² + C

∫(lntanx)/(sin2x) dx =(1/2)∫(lntanx)/(sinxcosx) dx d(lntanx)=(sec²x/tanx)dx=dx/(sinxcosx) =(1/2)∫(lntanx)/(sinxcosx)·sinxcosxd(lntanx) =(1/2)∫(lntanx)d(lntanx) =(1/2)(lntanx)²/2+C =(1/4)(lntanx)²+C

见图

lim(x→π/2)(tanx)^sin2x =e^[lim(x→π/2)sin2xlntanx =e^[lim(x→π/2)sin2x/(1/lntanx)] =e^[lim(x→π/2)2cos2xtanx/sec^2x...

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