∫[√(1-sin2x) ]dx = ∫ |sinx-cosx| dx.
将区间[0,π/2]分成[0,π/4]和[π/4,π/2].
because 0 < x < π/4 ,cosx > sinx,|sinx - cosx| = cosx - sinx.
π/4 < x < π/2,sinx > cosx,|sinx - cosx| = sinx - cosx.
所以,原式=∫(sinx-cosx)dx(区间[π/4,π/2])+∫(cosx-sinx)dx(区间[0,π/4])=...
∫(0-->π/2) |sinx-cosx|dx =/= ∫(0→π/2)(sinx-cosx)dx