4（2p+3q)^2 - 9（3p-q)^2
=[2(2p+3q) + 3(3p-q)][2(2p+3q) - 3(3p-q)]
=(4p+6q+9p-3q)(4p+6q-9p+3q)
=(13p+3q)(9q-5p)