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parabola-powered calculator

Drag a line from 1 black circle to another 1 from the opposite side.

The place where the line crosses the vertical number scale is the product of the two numbers you have chosen.

Surprised? Even if you're familiar with this curve called a parabola, you probably didn't realize it could help you with multiplication. Numbers and geometric patterns are inextricably linked, often in suprising ways.

Here, the line intercepts the vertical axis at a point known as the geometric mean of the two numbers you chose - effectively multiplying them together.

The above picture is the exhibition from Exploratorium in SF, I replicated it using JavaScript.