数学题(求解)

首先将上式展开，得
z=8x^(3)+70xy^+44x^y+25y^(3)
dz=(24x^+70y^+88xy)dx+(140xy+44x^+75y^)dy

(2x + 5y)^(2x + y) (((2x + y) (2 dx + 5 dy))/(2 x + 5 y) + (2 dx + dy)*Log[2x + 5y])

设u=2x+5y, v=2x+y, 则z=u^v;
dz=z_x dx+z_y dy
=(z_u*u_x+z_v*v_x)dx+(z_u*u_y+z_v*v_y)dy
=....
m_n表示m对n求偏导