练习13 四. 3.L=x = xInx.(y=x”mx孙2-1 =x"Ix:(y2)2= ylnx·y 四4.F(x,)≈ f(s)ds+e dx OF ax f∫(xy)·y OF f(xy)·x-∫(y) ay K心练习1.3 四. 3. , z y u = x =   y u x x  z y ln y z ( y ) 1 ln − =  y z x x zy z =   y u x x  z y ln z z ( y ) x x y y y z z = ln  ln 四. 4. =  +  1 0 2 F(x, y) f (s)ds e dx xy x y f xy y x F =    ( ) f (xy) x f ( y) y F =  −  