The first step in solving the quadratic equation \((X + 10)^2 - 25 = 36\) is to isolate the squared term. To do this, you can start by adding 25 to both sides of the equation:
\[ (X + 10)^2 - 25 + 25 = 36 + 25 \]
This simplifies to:
\[ (X + 10)^2 = 61 \]
From there, you can proceed to take the square root of both sides and solve for \(X\).