表达中 e 表示偏导1.dz/dt=ez/ex*dx/dt+ez/ey*dy/dt =(2x+y)*2t+(2y+x)*1=4t^3+3t^2+2t2.dz/dx=ez/ey*dy/dx+ez/ex=[sec(x+y)]^2*e^x+[sec(x+y)]^2=[sec(x+y)]^2*(e^x+1)
