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If the first term of an arithmetic sequence equals the second term minus the third, and the fourth term is 8, what is the first term?

 Sep 6, 2021
 #1
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a1 + 3d  = 8      8-3d = a1

a1 = a2 - (a2 +d)      - a1 =  d    

 

8 - (3*-a1) =a1

                                                 8 + 3a1=a1

                                                 8 = -2a1

                                                 a1 = -4               d = 4  

 

-4   0    4     8

 Sep 6, 2021

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