Given

F( x, y ,z) = 2x + 3y^2 + yz,

find Directional derivative of F at ( 2 , -1, 5) along the direction given by line x = y = ( z / 2).

-----------------------------------------------------------------------

Directional derivative Formula = ∇f · u

i grad the F and achieve ( 2, 6y + z , y).

then i sub ( 2 , -1, 5) which is the point into it <--- is this correct ?

what is the u then ?

many thanks