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A sequence is defined by a_{n + 1} = a_n + 2n, and a_1 = 4.  What is the sum of the seventh term and eighth term?

 May 23, 2020
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A sequence is defined by a_{n + 1} = a_n + 2n, and a_1 = 4. 

 

This recursion can be written as:  an = a1 + (n-1)*n

 

You can easily obtain a7 + a8 from this.

 May 23, 2020

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