Ấn nhầm :v
a) \(4x^4-21x^2y^2+y^4\)
\(=\left(2x^2\right)^2-2\cdot2x^2\cdot y^2+y^2-25x^2y^2\)
\(=\left(2x^2-y^2\right)^2-\left(5xy\right)^2\)
\(=\left(2x^2-5xy-y^2\right)\left(2x^2+5xy-y^2\right)\)
b) \(x^5-5x^3+4x\)
\(=x^5-4x^3-x^3+4x\)
\(=x^3\left(x^2-4\right)-x\left(x^2-4\right)\)
\(=\left(x^2-4\right)\left(x^3-x\right)\)
\(=x\left(x-2\right)\left(x+2\right)\left(x^2-1\right)\)
\(=x\left(x-2\right)\left(x+2\right)\left(x-1\right)\left(x+1\right)\)
\(4x^4-21x^2y^2+y^4\)
\(=\left(2x^2\right)^2+2.2x^2.y^2+\left(y^2\right)^2-25x^2y^2\)
\(=\left(2x^2+y^2\right)^2-\left(5xy\right)^2\)
\(=\left(2x^2-5xy+y^2\right)\left(2x^2+5xy+y^2\right)\)
\(x^5-5x^3+4x\)
\(=x\left[x^4-5x^2+4\right]\)
\(=x\left[x^4-x^2-4x^2+4\right]\)
\(=x\left[x^2\left(x-1\right)-4\left(x^2-1\right)\right]\)
\(=x\left(x^2-1\right)\left(x^2-4\right)=x\left(x-1\right)\left(x+1\right)\left(x-2\right)\left(x+2\right)\)
