\(A=x^2+x^3+x=x\left(x^2+x+1\right)\)
\(B=xy+3x+7y+21=x\left(y+3\right)+7\left(y+3\right)=\left(y+3\right)\left(x+7\right)\)
\(C=\left(x+2\right)^2+4x+8=\left(x+2\right)^2+4\left(x+2\right)=\left(x+2\right)\left(x+2+4\right)=\left(x+2\right)\left(x+6\right)\)
\(D=x^2-8x+15=x\left(x-3\right)-5\left(x-3\right)=\left(x-3\right)\left(x-5\right)\)
\(E=x^2-30x+200=x\left(x-20\right)-10\left(x-20\right)=\left(x-20\right)\left(x-10\right)\)
\(A=x\left(x+x^2+1\right)\\ B=\left(x+3\right)\left(y+7\right)\\ C=\left(x+2\right)\left(x+6\right)\\ D=\left(x-3\right)\left(x-5\right)\\ E=\left(x-10\right)\left(x-20\right)\)
