36(m+n)²-25(m-n)²
=[6(m+n)]²-[5(m-n)]²
=[6(m+n)+5(m-n)]*[6(m+n)-5(m-n)]
=(6m+6n+5m-5n)(6m+6n-5m+5n)
=(11m+n)*(m+11n)
=11m²+122mn+11n²