$$( \frac { - 5 } { 8 } + \frac { 9 } { 8 } ) + \frac { 13 } { 8 } = \frac { - 5 } { 8 } + ( \frac { 9 } { 8 } + \frac { 13 } { 8 } )$$
$\text{true}$
$$-\frac{5}{8}+\frac{9}{8}+\frac{13}{8}=\frac{-5}{8}+\frac{9}{8}+\frac{13}{8}$$
$$\frac{-5+9}{8}+\frac{13}{8}=\frac{-5}{8}+\frac{9}{8}+\frac{13}{8}$$
$$\frac{4}{8}+\frac{13}{8}=\frac{-5}{8}+\frac{9}{8}+\frac{13}{8}$$
$$\frac{4+13}{8}=\frac{-5}{8}+\frac{9}{8}+\frac{13}{8}$$
$$\frac{17}{8}=\frac{-5}{8}+\frac{9}{8}+\frac{13}{8}$$
$$\frac{17}{8}=-\frac{5}{8}+\frac{9}{8}+\frac{13}{8}$$
$$\frac{17}{8}=\frac{-5+9}{8}+\frac{13}{8}$$
$$\frac{17}{8}=\frac{4}{8}+\frac{13}{8}$$
$$\frac{17}{8}=\frac{4+13}{8}$$
$$\frac{17}{8}=\frac{17}{8}$$
$$\text{true}$$
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