Question 3
In the equilateral triangle $ABC$, $M,N$ are the midpoints of the sides $AB,AC$, respectively. The line $MN$ intersects the circumcircle of $\triangle ABC$ at $K$ and $L$ and the lines $CK$ and $CL$ meet the line $AB$ at $P$ and $Q$, respectively. Prove that $PA^2\cdot QB=QA^2\cdot PB$.