Find the sum of the first 90 terms of an AP whose first term is 5 and 90th term Is 625
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Answer:
a = 5
l = 625
d = ?
n = 90
l = a+(n-1)d
625 = 5+(90-1)d
625 = 5 + 59d
620/59 = d (for extra)
S90 = n/2[a+ l)
s90 = 90/2[5 + 625]
= 45[630]
= 28350
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