\(=4x^4+21x^2y^2+y^4-25x^2y^2\)

\(\left(2x^2+y^2\right)-\left(5xy\right)^2\)

\(\left(2x^2+y^2-5xy\right)\left(2x^2+y^2+5xy\right)\)

$=4{}^{}+21{}^{}{}^{}+{}^{}-25{}^{}{}^{}$

$\left(2{}^{}+{}^{}\right)-{}^{}$

$\left(2{}^{}+{}^{}-5xy\right)\left(2{}^{}+{}^{}+5xy\right)$

bạn ơi cái chỗ 21x^2 ? y^2 là dấu cộng hay trừ vậy?

Nó là 1 á

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

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

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

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

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

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

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

\(21x-7y=7\left(3x-y\right)\)

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

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

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

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

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

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

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

4x^4+4x^2y^2+y^4-25x^2y^2

=(2x^2+y^2)^2-(5xy)^2

=(2x^2+y^2-5xy)(2x^2+y^2+5xy)