The sum ∑ k = 1 20 1 + 2 + 3 + … + k is ___________.

Question

The sum &#8721; k = 1 20 1 + 2 + 3 + &#8230; + k is ___________.

Aicharya · Accepted Answer

&#160; &#160; &#160; &#160; &#8721; k = 1 20 k ( k + 1 ) 2 = 1 2 &#8721; k = 1 20 k 2 + k = 1 2 20 21 41 6 + 20 21 2 = 1 2 420 &#215; 41 6 + 20 &#215; 21 2 = 1 2 2870 + 210 = 1540

The sum &#8721; k = 1 20 1 + 2 + 3 + &#8230; + k is ___________.

Solution

The sum ∑ k = 1 20 1 + 2 + 3 + … + k is ___________.