(3x−5y+4)(9x2+25y2+15xy−20y+12x+16)
=(3x−5y+4)(9x2+25y2+16+15xy−20y+12x)
Weknowthat
(a+b+c)(a2+b2+c2−ab−bc−ca)=a3+b3+c3−3abc
Here,a=3x,b=5y,c=4
∴(3x−5y+4)(9x2+25y2+16+15xy−20y+12x)=(3x)3+(5y)3+43−3(3x)(5y)(4)
∴(3x−5y+4)(9x2+25y2+16+15xy−20y+12x)=27x3+125y3+64−180xy