Question 888309
General term of arithmetic sequence is a+(n-1)d  using n as the index and d as the common difference.
The initial term is a.
n=7, term is 11;
n=20, term is -41.


{{{a+(7-1)d=11}}}
{{{a+6d=11}}}
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{{{a+(20-1)d=-41}}}
{{{a+19d=-41}}}
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Start with Elimination Method to first find d.
{{{1+19d-(a+6d)=-41-11}}}
{{{19d-6d=-52}}}
{{{13d=-52}}}
{{{highlight(d=-4)}}}

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Using the n=7 equation, {{{a=-6d+11}}}
{{{a=-6(-4)+11}}}
{{{highlight(a=35)}}}


General term is {{{highlight(highlight(35+(n-1)(-4)))}}}.
You can find whichever term you want.