What equation can be solved to find one of the missing side lengths in the triangle

Just do Pythagorean theorem

A^2 + B^2 = C^2

A and B are the legs. C is the hypotenuse the dialogue slanted part.

The vertical axis represents the velocity of the object. This probably sounds obvious, but be forewarned—velocity graphs are notoriously difficult to interpret. People get so used to finding velocity by determining the slope—as would be done with a position graph—they forget that for velocity graphs the value of the vertical axis is giving the velocity.

Try sliding the dot horizontally on the example graph below to choose different times and see how the velocity changes.

Explanation: