∫ x f(x²) dx = x e^x
x f(x²) = d(x e^x)/dx = e^x + x e^x,两边求导
f(x²) = (e^x)/x + e^x,代入x = √x
f(x) = (e^√x)/√x + e^√x
= (e^√x)(1 + 1/√x)