How is the sum expressed in sigma notation?
13 + 21 + 29 + 37 + 45
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The numbers increase by 8 each time; this is the slope so the formula will have the form 8i + .
To find the , put in 1 for i and see that your answer is 8, not 13; so, you will need 5 more.
[This is also true if you put in2 for i and see that your answer is 16, not 21.]
So, the formula is: 8i + 5