展开 ((n-1)*n)/2

解答

展开

\frac{( n - 1 ) \cdot n}{2}

\frac{n ^{2}}{2} - \frac{n}{2}

求解步骤

\frac{( n - 1 ) n}{2}

乘开

(n - 1) n : n^{2} - n

= \frac{n ^{2} - n}{2}

使用分式法则:

\frac{a \pm b}{c} = \frac{a}{c} \pm \frac{b}{c}

\frac{n ^{2} - n}{2} = \frac{n ^{2}}{2} - \frac{n}{2}

= \frac{n ^{2}}{2} - \frac{n}{2}

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