A=∫cosx/（sinx+cosx)dx
B=∫sinx/(sinx+cosx)dx
A+B=∫(cosx+sinx)/(sinx+cosx)dx =∫dx =x+c (1)
A-B=∫(cosx-sinx)/(sinx+cosx)dx =∫(d(cosx+sinx)/(sinx+cosx)=ln(cosx+sinx)+c (2)
[(1)+(2)]/2得：
A=∫cosx/(sinx+cosx)dx =x/2+1/2*ln(cosx+sinx)+c
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