f(x,y)=e^(-x)sin(x+2y)则df(0,π/4)值是多少有有没得人回答下么

Question

f(x,y)=e^(-x)sin(x+2y)则df(0,π/4)值是多少有 有没得人回答下么

Answer 1

fx= -e^(-x)sin(x+2y)+e^(-x)cos(x+2y)= -1
fy=e^(-x)*2*cos(x+2y)=0
df=fx*dx+fy*dy=-dx+0dy=-dx