Question 1147297
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{{{nC3+nC2+nC1}}} =<br>
{{{(n(n-1)(n-2))/6 + (n(n-1))/2+ n/1}}} =<br>
{{{(n^3-3n^2+2n)/6 + (n^2-n)/2 + n}}} =<br>
{{{(n^3-3n^2+2n)/6 + (3n^2-3n)/6 + 6n/6}}} =<br>
{{{(n^3-3n^2+2n+3n^2-3n+6n)/6}}} =<br>
{{{(n^3+5n)/6}}} =<br>
{{{(n(n^2+5))/6}}}<br>