Thanks, i just went back and checked the back of the book, the answer is supposed to be -8*sqrt(2) not -8/sqrt(2). Also i didn't notice that -16/sqrt(2) is the same thing as -8*sqrt(2). Thanks for the help.
Homework Statement
Find the directional derivative of f at P in the direction of a.
f(x,y)=y2lnx; P(1,4); a= -3i + 3j
Homework Equations
The Attempt at a Solution
I first normalized the vector and got an = -3/(18)^1/2 + 3/(18)^1/2
Then i took the partial derivative and multiplied...