The operation \(x y = x + y^2\) is defined as adding \(x\) to the square of \(y\).

To find the value of \((2 3) 5\), we can follow these steps:

1. Evaluate the inner operation first:

\(2 3 = 2 + 3^2 = 2 + 9 = 11\).

2. Now, use the result from step 1 and the second operand \(5\) for the outer operation: \(11 5 = 11 + 5^2 = 11 + 25 = 36\).

So, the value of (2 3) 5 is 36.