# Directional Derivative Calculator

The calculator will find the directional derivative (with steps shown) of the given function at the point in the direction of the given vector.

Enter a function:
Enter a point:
Enter a point, for example, (1, 2, 3) as x,y,z=1,2,3, or simply 1,2,3, if you want the order of variables to be detected automatically.
Enter vector $\vec{u}$: ()
As comma-separated coordinates, for example, 2i-3j should be entered as 2,-3.

If the calculator did not compute something or you have identified an error, or you have a suggestion/feedback, please write it in the comments below.

## Solution

Your input: find the directional derivative of $e^{x} + \sin{\left(y z \right)}$ at $\left(x,y,z\right)=\left(3,0,\frac{\pi}{3}\right)$ in the direction of the vector $\vec{u}=\left(2,3,6\right)$

Find the gradient of the function and evaluate it at the given point:

$\nabla \left(e^{x} + \sin{\left(y z \right)}\right)|_{\left(x,y,z\right)=\left(3,0,\frac{\pi}{3}\right)} = \left(e^{3},\frac{\pi}{3},0\right)$ (for steps, see gradient calculator)

Find the length of the vector: $\left|\vec{u}\right|=\sqrt{\left(2\right)^2+\left(3\right)^2+\left(6\right)^2}=7$

To normalize the vector, divide each component by the length:

$\vec{u}$ becomes $\left(\frac{2}{7},\frac{3}{7},\frac{6}{7}\right)$.

Finally, the directional derivative is the dot product of the gradient and the normalized vector:

$D\left(e^{x} + \sin{\left(y z \right)}\right)_{\vec{u}}\left(3,0,\frac{\pi}{3}\right)=\left(e^{3},\frac{\pi}{3},0\right) \cdot \left(\frac{2}{7},\frac{3}{7},\frac{6}{7}\right) = \frac{\pi + 2 e^{3}}{7}$ (for steps, see dot product calculator)

Answer: $D\left(e^{x} + \sin{\left(y z \right)}\right)_{\vec{u}}\left(3,0,\frac{\pi}{3}\right)=\frac{\pi + 2 e^{3}}{7} \approx 6.1875237857093$