Find the function to which the given series converges within its interval of convergence. Use exact values.

x3x42x53x64x75x86=\displaystyle -{x}^{{3}}-\frac{{x}^{{4}}}{{2}}-\frac{{x}^{{5}}}{{3}}-\frac{{x}^{{6}}}{{4}}-\frac{{x}^{{7}}}{{5}}-\frac{{x}^{{8}}}{{6}}-\ldots\ldots=