In the solution for A tangent is… we had the following,

When we “zoom in” to a point on a curve, it often looks like a straight line. If so, then we can draw that straight line. If we then zoom out again, we will discover that we have drawn the tangent to the curve at that point. This is what a tangent is.

How can we use this to find the gradient of the tangent line?

How do we find the gradient of a straight line?