Bài 8:
a: \(9x^2+30x+25=\left(3x+5\right)^2\)
\(\dfrac{4}{9}x^4-16x^2=4x^2\left(\dfrac{1}{3}x-2\right)\left(\dfrac{1}{3}x+2\right)\)
b: \(\dfrac{12}{5}x^2y^2-9x^4-\dfrac{4}{25}y^4\)
\(=-\left(9x^4-\dfrac{12}{5}x^2y^2+\dfrac{4}{25}y^4\right)\)
\(=-\left(3x^2-\dfrac{2}{5}y^2\right)^2\)
Bài 9:
b: \(x^3-3x^2+3x-1=\left(x-1\right)^3\)