A curve, y = x · x, on axes x and y with x ticks 2, 3 and 4 and y ticks 9 and 16. Teal secants from the right and blue-violet secants from the left close in on a gold tangent at (3, 9). A small triangle on the first right secant shows run 1 and rise 7. Notes list the right slopes 7, 6.5, 6.25 and the left slopes 5, 5.5, 5.75, heading to 6.

Slide the second point in from both sides. First secant: (16 + (−9)) ÷ (4 + (−3)) = 7. The slopes squeeze onto 6: the tangent at (3, 9). One step across is drawn longer than one step up.