y=aepx+beqx
Differentiate on both sides w.r.t x
dydx=y1=apepx+bqeqx
d2ydx2=y2=ap2epx+bq2eqx
y2−(p+q)y1+pqy=ap2epx+bq2eqx−(p+q)(apepx+bqeqx)+pq(aepx+beqx)
=0
∴y=y2−(p+q)y1+pqy=0