\(x^{n+3}+x^n=x^n.x^3+x^n=x^n\left(x^3+1\right)=x^n\left(x+1\right)\left(x^2-x+1\right)\)
\(x^{n+3}+x^n=x^n\left(x^3+1\right)=x^n\left(x+1\right)\left(x^2-x+1\right)\)
\(x^{n+3}+x^n=x^n\left(x^3+1\right)=x^n\cdot\left(x+1\right)\left(x^2-x+1\right)\)