what happens when we have an inequality in place of the = sign in a quadratic equation?
Solving it as an equality provides bounds on its validity.
For example:
y^2 - 4 < 0
Solve Y^2 - 4 = 0 to get Y = 2 and Y = -2
Then -2 < y < 2
Similarly, if y^2 - 4 > 0 then y < -2 and y > 2
