(m+n)²-9n²
=(m+n+3n)(m+n-3n)
=(m+4n)(m-2n)
(2p+3q)²-(p-q)²
=[(2p+3q)+(p-q)][(2p+3q)-(p-q)]
=(3p+2q)(p+4q)
(2a+b)²-(2b-a)²
=[(2a+b)+(2b-a)][(2a+b)-(2b-a)]
=(a+3b)(3a-b)