Math, asked by l5i5zagarresh, 1 year ago

Find the number of terms of the AP 63,60,57,..... so that their sum is 693.Explain the double answer. can sumbody help me fast with the double answer part....

Answers

Answered by SARDARshubham
1
In the given A.P ;
63,60,57...
a = 63
d = 60-63 = -3
Sn = 693
n = ?

Sn = (n/2)×[2a+(n-1)d]
693 = (n/2)×([2×63)+(n-1)(-3)]
1386 = n(126 -3n+3)
1386 = 126n -3n^2+3n
3n^2 -129n +1386 = 0
n^2 -43n + 462 =0
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