Respuesta :

Well, lets imagine that the gradient of f =[tex](x1,y1) at (1,2)[/tex]
Since that, we can found the hence using this way : [tex](x1,y1) . (1,1)/sqrt(2) = 2 sqrt(2)[/tex] with the result of : [tex]x1+y1 = 4[/tex]
According to the 2nd directional derivative we can have [tex]-2 y1 =-6[/tex]
Now it is not difficult to conclude that hence the gradient of f at (1,2) is (1,3) and we have to compute [tex](1,3) . (-1,-2) [/tex] and divide by sqrt(5). 
Finally, here is the answer that you will get in the end 
−(7/5√)
ACCESS MORE