SOLUTION: An A.p has 15 terms and a common difference of -3 find its first and last terms if its sum -120
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Question 1053000: An A.p has 15 terms and a common difference of -3 find its first and last terms if its sum -120
Answer by ewatrrr(24785) (Show Source): You can put this solution on YOUR website!
S = (n/2)(2a + (n-1)d)
-120 = 15/2 (2a + 14(-3))
-16 = 2a - 42
26 = 2a
a1 = 13
a15 = 13 + (-42)
a15 = -29
Checking
-120 = 15(13-29)/2 = 15(-16)/2 = -120 CHECKS
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