These are images from calculus.
The first rock shows boxes trying to estimate the area under a curve. This gives us a very rough idea of the area, but we can imagine smaller and smaller boxes could give us a better idea of the area.
The second rock shows the integral, which imagines that we have found the exact area under the cuve by imagining infinitely many boxes matching the exact area under the curve.
Here's a challenge for calculus students. If the images on the two rocks are related, what would be an other name for "a?"
Another name for "b?"