Find the directional derivative of f at P in the direction of a.
f(x,y)=y2lnx; P(1,4); a= -3i + 3j
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 it by the vector
y2/X(-3/181/2) + 2(y)lnx(3/181/2
Ln(1) = 0 so the whole right side is gone, and after i plug in 1 and 4 on the right side i get -16/21/2. The answer should be -8/21/2. I've done 5 problems like this now and each time i'm off by a negative or a factor or something like that. What am i doing wrong?