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令t=x/2
(1+sinx+cosx)/(1+sinx-cosx)
=(1+2sintcost+2cos^2(t)-1)/(1+2sintcost-1+sin^2(t))
=(sintcost+costcost)/(sintcost+sintsint)
=cost(sint+cost)/[sint(cost+sint)]
=cost/sint
=ctgt
=ctg(x/2)
(1+sinx+cosx)/(1+sinx-cosx)
=(1+2sintcost+2cos^2(t)-1)/(1+2sintcost-1+sin^2(t))
=(sintcost+costcost)/(sintcost+sintsint)
=cost(sint+cost)/[sint(cost+sint)]
=cost/sint
=ctgt
=ctg(x/2)
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