\(\frac{x^2-11}{2}+1+\frac{x^2-13}{4}+1=\frac{x^2-15}{6}+1+\frac{x^2-16}{7}+1\)
\(\frac{x^2-9}{2}+\frac{x^2-9}{4}-\frac{x^2-9}{6}-\frac{x^2-9}{7}=0\)
\(\left(x^2-9\right)\left(\frac{1}{2}+\frac{1}{4}-\frac{1}{6}-\frac{1}{7}\right)=0\)
\(Do:\left(\frac{1}{2}+\frac{1}{4}-\frac{1}{6}-\frac{1}{7}\right)\ne0\)
\(\Rightarrow x^2-9=0\) => x=3 hoặc x=-3