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The first term of an arithmetic sequence is -8. Find the 20th term if the sum of the first 20 terms is 790.

 Aug 29, 2021
 #1
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790==20/2 * [2*(-8) + 19D], solve for D

 

D==5 - this is the common difference

 

20th term ==[- 8 + 5 * (20 - 1) ]

                   ==[- 8 +  (5 * 19) ]

                   ==[ - 8 +   95]

                   == 87 - the 20th term

Your sequence looks like this:

 

-8 , -3 , 2 , 7 , 12 , 17 , 22 , 27 , 32 , 37 , 42 , 47 , 52 , 57 , 62 , 67 , 72 , 77 , 82 , 87 , >>Number of terms = 20>>Total Sum == 790

 Aug 29, 2021

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