DS questions rarely involve this many variables, but when a DS question is this "crazy looking" the solution can usually be found by TESTing VALUES and keeping everything really 'simple'
Here, we're asked if (X/P)(P^2 + Q^2 + R^2) = XP + YQ + ZR. This is a YES/NO question.
The first thing that you should notice is that the variables Y and Z only appear on the right side of the equation/question. Their respective values will have a great impact on whether the answer to the question is YES or NO.
Fact 1: Q^2 = R^2
Let's TEST VALUES (and keep it simple!)
EVERY variable = 0, then the answer to the question is YES.
X, P, Q and R = 1
Y = Z = 2, then the answer to the question is NO.
Fact 1 is INSUFFICIENT
Fact 2: YQ = ZR
Notice how BOTH TESTs from Fact 1 ALSO fit Fact 2.....This gives us a YES answer and a NO answer here as well.
Fact 2 is INSUFFICIENT
Combined, we have the same two TESTs that fit BOTH Facts and provide 2 different answers.
GMAT assassins aren't born, they're made,