Hallo,
f(x.y)= 4x^5+2x+5xy−4y^4
fx=20x^4 +2 +5y
fy= 5x -16y^3
---->Punkt einsetzen:
fx(2, -1)= 317
fy(2, -1)= 26
z0= 4 *2^5 +2*2 -10 -4*1
z0=118
z=z0+fx(x0,y0) (x-x0) +fy(x0,y0) (y-y0)
z=118 +317( x-2) +26(y+1)
z= 118 +317x -634+26y+26
z=317x +26y -490