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Skal derivere f(x,y,z)= (x*z)/(y+z) mhp. z, altså d/dz, men får stadig feil svar, noen som kunne ta den?

df/dz

= [xz/(y + z)]' ([g(x,y,z)]' betyr her dg/dz)

= x*[z/(y + z)]'

= x [(z)'*(y + z) - z*(y + z)'] / (y + z)[sup]2[/sup]

= x [1*(y + z) - z*1] / (y + z)[sup]2[/sup]

= xy / (y + z)[sup]2[/sup].

Takk!
Hva med denne:
df/dy x[sup](y*lnz)[/sup] ?

d/dy [x[sup]y*lnz[/sup]] = d/dy [(x^lnz)[sup]y[/sup]] = (x^lnz)[sup]y[/sup] * ln(x[sup]lnz[/sup]) = lnz*lnx*x[sup]y*lnz[/sup].