Question 932735
7,9,11,13....
<pre>
{{{a[1]=7}}}, {{{d=2}}}

{{{a[n]=a[1]+(n-1)d}}}

{{{a[n]=7+(n-1)2}}}

{{{a[n]=7+2n-2}}}

{{{a[n]=5+2n}}}

Find sigma notation for the sum of the first twenty terms

{{{sum((5+2n),n=1,20)}}}

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I think that's all you're supposed to do.  We can go further
and evaluate that sum, which you'll probably have next semester:

{{{sum((5),n=1,20)}}}{{{""+""}}}{{{sum((2n),n=1,20)}}}

{{{5sum((1),n=1,20)}}}{{{""+""}}}{{{2sum((n),n=1,20)}}}

{{{5*20+2(20(20+1))/2}}}

{{{100+(20*21)}}}

{{{100+420}}}

{{{520}}}

Edwin</pre>