\(\left(x-4\right)^2-9^2=\left(x-13\right)\left(x+5\right)\)

\(=x^2\left(8x-3\right)-\left(8x-3\right)=\left(8x-3\right)\left(x^2-1\right)\)

Lời giải:

$(x^3-2xy+3x^2)(x-2y)=x(x^2-2xy+3x)(x-2y)$

\(4x^4-21x^2+1\)

\(=\left(2x^2\right)^2+2.2x^2+1-25x^2\)

\(=\left(2x^2+1\right)^2-\left(5x\right)^2\)

\(=\left(2x^2+1-5x\right)\left(2x^2+1+5x\right)\)

\(4x^4-21x^2+1=\left(2x^2-\frac{21}{4}\right)^2-\frac{425}{16}.\)

−5𝑥^2−8𝑥+4

\(=\left[2\left(x-1\right)-3x\right]\left[2\left(x-1\right)+3x\right]\\ =\left(2x-2-3x\right)\left(2x-2+3x\right)\\ =\left(-2-x\right)\left(5x-2\right)\\ =\left(x+2\right)\left(2-5x\right)\)

\(4\left(x-1\right)^2-9x^2=\left(2x-2\right)^2-\left(3x\right)^2=\left(2x-2-3x\right)\left(2x-2+3x\right)=\left(-x-2\right)\left(5x-2\right)=-\left(x+2\right)\left(5x-2\right)=\left(x+2\right)\left(2-5x\right)\)

\(3x^3-21x^2+27x=3x\left(x^2-7x+9\right)\)

\(3x^3-21x^2+27x=3x\left(x^2-7x+9\right)\)

4x⁴ - 21 x²y² + y⁴ 

= (4x⁴ + 4x²y² + y⁴) - 25x²y² 

=  [(2x²)² + 2x² . 2 . y² + (y²)²] - 25x²y²

= (2x² + y²) - 25x²y² 

= (2x² + y² - 5xy) (2x² + y² + 5xy)

\(7x^3y-3xyz-21x^2+9z\)

\(=\left(7x^3y-21x^2\right)-3xyz+9z\)

\(=7x^2\left(xy-3\right)-3z\left(xy-3\right)\)
\(=\left(7x^2-3z\right)\left(xy-3\right)\)
 

\(7x^3y-3xyz-21x^2+9z\)

\(=\left(7x^3y-21x^2\right)+\left(-3xyz+9x\right)\)

\(=7x^2\left(xy-3\right)-3z\left(xy-3\right)\)

\(=\left(xy-3\right)\left(7x^2-3z\right)\)