Find the value of y.

  y = √55

Step-by-step explanation:

All the triangles are similar, so the ratio of short side to hypotenuse is the same for all:

  5/y = y/(5+6)

  y^2 = 55

  y = √55

Comment on the geometry

There are three "geometric mean" relationships that apply to this geometry.

If you were aware of the last of these relationships, you could write down the answer without any "work."

  y = √(5(5 +6)) = √55

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The geometric mean is the n-th root of the product of n numbers. When there are 2 numbers, it is the square root of their product.