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....
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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
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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