a) \(x^3-9x^2+15x+25\)
\(=x^3+x^2-10x^2-10x+25x+25\)
\(=x^2\left(x+1\right)-10x\left(x+1\right)+25\left(x+1\right)\)
\(=\left(x+1\right)\left(x^2-2.x.5+25\right)=\left(x+1\right)\left(x-5\right)^2\)
b) \(x^8-4x^2-11x+30:\text{đề sai thì phải bạn ạ!}\)
c) \(x^4+x^3-22x^2+15x-36\)
\(=\left(2x^4-6x^3\right)+\left(7x^3-21x^2\right)-\left(x^2-3x\right)+12x-36\)
\(=2x^3\left(x-3\right)+7x^2\left(x-3\right)-x\left(x-3\right)+12\left(x-3\right)\)
\(=\left(x-3\right)\left(2x^3+8x^2-x^2-x+12\right)\)
\(=\left(x-3\right)\left[\left(2x^3+8x^2\right)-\left(x^2+4x\right)+3\left(x+4\right)\right]\)
\(=\left(x-3\right)\left[2x^2\left(x+4\right)-x\left(x+4\right)+3\left(x+4\right)\right]\)
\(=\left(x-3\right)\left(x+4\right)\left(2x^2-x+3\right)\)
