`4(x^2+15x+50)(x^2+18x+72)-3x^2`
`=4[(x+5)(x+10)]\times [(x+6)(x+12)]-3x^2`
`=4[(x+5)(x+12)]\times [(x+6)(x+10)]-3x^2`
`=4(x^2+17x+60)(x^2+16x+60)-3x^2`
Đặt `x^2+16x+60=a`
`4a.(a+x)-3x^2`
`=4a^2+4ax-3x^2`
`=(2a-x)(3x+2a)`
`=(2x^2+31x+120)(2x^2+35x+120)`
`=(2x+15)(x+8)(2x^2+35x+120)`