ABC is an acute triangle(all the three angles are acute).
D,E,F are points on BC,CA,AB respectively such that AD,BE,CF are the altitudes of the triangle.
FP is perpendicular to BC, P lying on BC
FQ is perpendicualr to AC, Q lying on AC
FM is perpendicular to AD, M lying on AD
FN is perpendicualr to BE, N lying on BE
Prove that P,Q,M,N are collinear points.