# Proving a Function is Less than a Value

I'm working on a multipart problem and I've been asked to prove that a value W < 0.5.

I worked out W and reached $$W = \frac{\sqrt{X1*X2*Y1*Y2}}{X1*Y1+X2*Y2+X1*Y2}$$

but I'm not sure how to progress from here to prove that W < 0.5. Though I placed values into the equation using excel and can see that it will indeed be a fraction.