Solve f(x)=x^15x^5+x

$$f ( x ) = x ^ { 15 } x ^ { 5 } + x$$

Factor

$$x\left(x+1\right)\left(x^{18}-x^{17}+x^{16}-x^{15}+x^{14}-x^{13}+x^{12}-x^{11}+x^{10}-x^{9}+x^{8}-x^{7}+x^{6}-x^{5}+x^{4}-x^{3}+x^{2}-x+1\right)$$

Solution Steps

Factor out x.

$$x\left(x^{14}x^{5}+1\right)$$

Consider x^{19}+1. By Rational Root Theorem, all rational roots of a polynomial are in the form \frac{p}{q}, where p divides the constant term 1 and q divides the leading coefficient 1. One such root is -1. Factor the polynomial by dividing it by x+1.

$$\left(x+1\right)\left(x^{18}-x^{17}+x^{16}-x^{15}+x^{14}-x^{13}+x^{12}-x^{11}+x^{10}-x^{9}+x^{8}-x^{7}+x^{6}-x^{5}+x^{4}-x^{3}+x^{2}-x+1\right)$$

Rewrite the complete factored expression. Polynomial x^{18}-x^{17}+x^{16}-x^{15}+x^{14}-x^{13}+x^{12}-x^{11}+x^{10}-x^{9}+x^{8}-x^{7}+x^{6}-x^{5}+x^{4}-x^{3}+x^{2}-x+1 is not factored since it does not have any rational roots.

$$x\left(x+1\right)\left(x^{18}-x^{17}+x^{16}-x^{15}+x^{14}-x^{13}+x^{12}-x^{11}+x^{10}-x^{9}+x^{8}-x^{7}+x^{6}-x^{5}+x^{4}-x^{3}+x^{2}-x+1\right)$$

Evaluate

$$x^{20}+x$$

Solution Steps

To multiply powers of the same base, add their exponents. Add 15 and 5 to get 20.

$$x^{20}+x$$