Imagine a triangle XOY which sides lie on x-axis and y-axis with hypotenuse XY of length 5 m.

Suppose the point X moves away from the (0,0) along x-axis with speed = 1 m per second. What speed the point Y will have when length of OX will be 3 m?

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If OX = 3, then OY = $\sqrt{5^2 - 3^2} = 4$. Unfortunately, this is all I did. Please, give a hint how to proceed?