$\"\"$

\

The equation of a tangent plane :

\

$\"\"$

\

$\"\"$

\

The function is $\"\"$ and the point is $\"\"$ .

\

Differentiate $\"\"$ partially with respect to $\"\"$ .

\

$\"\"$

\

Substitute the point $\"\"$ in above equation.

\

$\"\"$ .

\

Differentiate $\"\"$ partially with respect to $\"\"$ .

\

$\"\"$

\

Substitute the point $\"\"$ in above equation.

\

$\"\"$ .

\

$\"\"$

\

The equation of the tangent plane is $\"\"$

\

Substitute $\"\"$ and $\"\"$ in above equation.

\

$\"\"$

\

The equation of a tangent plane is $\"\"$ .

\

$\"\"$

\

The equation of a tangent plane is $\"\"$ .