is the term of an ap is 22 and the common difference is -4 and the sum of n terms is 64 find n
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Given d=-4
Sn =64 and a=22
Sn =n/2[2a+(n-1)d]
64=n/2[2(22)+(n-1)-4]
128=n[44-4n+4]
128=-4n sq +48n
4n sq - 48n +128 =0
4n sq - 16n - 32n + 128=0
4n(n-4)-32(n-4)=0
(n-4)(4n-32)=0
n=4 and n =8
n= 4(or)8
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