Question

What is the slope of a horizontal tangent line?

Answer 1

The slope of a horizontal tangent line is 0.

To calculate the slope of a straight line, we take a difference in the `y` dimension and divide it by the change in the `x` dimension of two points on the line:

`"slope" = (y_1 - y_2)/(x_1 - x_2)` assuming points `(x_1, y_1)` and `(x_2, y_2)` lie on the line

For a horizontal line `y_1 - y_2 = 0` so

`"slope" = 0/(x_1 - x_2) = 0`