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

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

x² - y² + 2yz - z²

= x² - (y² - 2yz + z²)

= x² - (y-z)²

= (x-y+z)(x+y-z) 

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

x²-x

= x(x-1)

\(x^4+x^2-27x-9\)

\(=x^4-27x+\left(x-3\right)\left(x+3\right)\)

\(=x\left(x^3-27\right)+\left(x-3\right)\left(x+3\right)\)

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

\(=\left(x-3\right)\left(x^3+3x^2+10x+3\right)\)

1) \(x^2+6y-9-y^2=x^2-\left(y^2-6y+9\right)=x^2-\left(y-3\right)^2=\left(x-y+3\right)\left(x+y-3\right)\)

2) \(9y^2-6y+1-25x^2=\left(3y\right)^2-2.3y+1-\left(5x\right)^2=\left(3y-1\right)^2-\left(5x\right)^2\)

\(=\left(3y-1-5x\right)\left(3y-1+5x\right)\)

3) \(a^2-9+6x-x^2=a^2-\left(x^2-6x+9\right)=a^2-\left(x-3\right)^2=\left(a-x+3\right)\left(a+x-3\right)\)

a) \(81-\left(3x+2\right)^2=9^2-\left(3x+2\right)^2=\left(9-3x-2\right)\left(9+3x+2\right)=\left(7-3x\right)\left(11+3x\right)\)

b) \(\left(7x-4\right)^2-\left(2x+1\right)^2=\left(7x-4-2x-1\right)\left(7x-4+2x+1\right)\)

\(=\left(5x-5\right)\left(9x-3\right)=15\left(x-1\right)\left(3x-1\right)\)

c) \(9\left(x-5y\right)^2-16\left(x+y\right)^2=\left[3\left(x-5y\right)-4\left(x+y\right)\right]\left[3\left(x-5y\right)+4\left(x+y\right)\right]\)

\(=\left(-x-19y\right)\left(7x-11y\right)\)

a: \(y^4+2y^3+y^2=y^2\left(y+1\right)^2\)

b: \(y^2+4y+3=\left(y+1\right)\left(y+3\right)\)

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