31. $\frac{1^{2}-2^{2}+3^{2}-4^{2}+5^{2}-6^{2}+7^{2}-8^{2}+9^{2}-10^{2}}{2^{0}+2^{1}+2^{2}+2^{3}+2^{4}+2^{5}+2^{6}+2^{7}}$ 的值是

The value of $\frac{1^{2}-2^{2}+3^{2}-4^{2}+5^{2}-6^{2}+7^{2}-8^{2}+9^{2}-10^{2}}{2^{0}+2^{1}+2^{2}+2^{3}+2^{4}+2^{5}+2^{6}+2^{7}}$ is
Reference answer: $-11 / 51$