计算下列式子:$\frac{5}{7}+\frac{2}{11}+\frac{-8}{7}+\frac{6}{11} $
已知: $\frac{5}{7}+\frac{2}{11}+\frac{-8}{7}+\frac{6}{11} $
步骤: 分母不同,先通分,
求7和11的最小公倍数(LCM),
7和11的最小公倍数是77
$\frac{5\times11}{ 7\times11} + \frac{2\times7}{ 11\times7} - \frac{8\times11}{ 7\times11} + \frac{6\times7}{ 11\times7}$
$\frac{55}{77} + \frac{14}{77} - \frac{88}{77} + \frac{42}{77}$
现在分母相同,直接计算分子,
$55 + 14 - 88 + \frac{42}{77}$
$\frac{111 - 88}{ 77}$
因此,表达式的值为 $\frac{23}{ 77}$ 。
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