Suppose Z = F(x, Y), F(1, 3)= 5 And $\nabla f ( 1,3 ) = 4 \vec { i } + 5 \vec { j }$

True/False

Suppose z = f(x, y), f(1, 3)= 5 and $\nabla f ( 1,3 ) = 4 \vec { i } + 5 \vec { j }$ the vector $- 4 \vec { i } + 5 \vec { j } + \vec { k }$ is perpendicular to the graph of f(x, y)at the point (1, 3).