积分 [e^x/2 *(cosx-sinx)] / √cosx dx
=积分2[1/2e^x/2*(cosx)^(1/2)-1/2e^x/2*sinx(cosx)^(-1/2)]dx
=积分[2e^x/2*（cosx）^(1/2)]'dx
=2e^x/2*（cosx）^(1/2)+C