a,\(15x^3y^4-20x^4y^3+30x^3y^3\)

=\(5x^3y^3\left(3y-4x+6\right)\)

b,\(x^2+10xy+25y^2\)

=\(x^2+2.x.5.y+\left(5y\right)^2\)

=\(\left(x+5y\right)^2\)

c,\(x^2-2xy+y^2-9z^2\)

=\(\left(x^2-2xy+y^2\right)-\left(3z\right)^2\)

=\(\left(x-y\right)^2-\left(3z\right)^2\)

=\(\left(x-y+3z\right)\left(x-y-3z\right)\)

chúc bn hok tốt