展开 ((n*(n-1)))/2

解答

展开

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

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

求解步骤

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

乘开

n (n - 1) : 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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