[m]6\cdot ln(1+x)=6\cdot \frac{x}{1!}-6\cdot \frac{x^2}{2!}+6\cdot \frac{x^3}{3!}-6\cdot \frac{x^4}{4!}+6\cdot \frac{x^5}{5!}+6\cdot \frac{x^6}{6!}+...[/m]
[m]a_{6}x^{6}=6\cdot \frac{x^6}{6!}[/m] ⇒ [m]a_{6}=6\frac{1}{6!}[/m] ⇒ [m]a_{6}=\frac{1}{120}[/m]