⑩天掌 Teaching Plan on Advanced Mathematics o 例1求z=x2+3xy+y2在点(1,2处的偏导数 解法103=2x+3y,0y az =3x+2y x az 2.1+3.2=8 az 3·1+2·2=7 x(1,2) Oy(1,2) 解法2 y=2=x2+6x+4 0 8 0x(1,2) (2x+6 x 2|x=1=1+3y+y (3+2y 7 y(1,2) tianjin polytechnic dmivendityTianjin Polytechnic University Teaching Plan on Advanced Mathematics 例1 求 2 2 z = x + 3x y + y 解法1 =   x z x (1,2) z    解法2 x (1, 2) z   在点(1,2)处的偏导数. y (1, 2) z   2x + 3 y , =   y z 3x + 2 y y (1, 2) z   6 4 2 = x + x + x=1 z 2 = 1+ 3y + y y=2 z