The tangent line to a single variable function was the line in two-dimensional space that represented the slope of the single variable function. Similarly, the tangent plane to a multivariable function is the plane in three-dimensional space that represents the slope of the multivariable function. To find the equation of the tangent plane, you need The slope of the function at the point of tangency in the direction of each independent variable (the partial derivative of the function with respect to each variable, evaluated at the point of tangency) The point of tangency