CBSE Class 10 Answered
the firstterm = 22 , the common difference = -4
thesum of n terms = Sn = n/ 2 { 2a + (n-1) d } = 64
= n / 2 { 2 x 22 + ( n - 1 ) x -4} = 64
n { 44 -4n + 4 } = 2 x 64 = 128
= 48 n - 4 n^2 - 128 = 0
4n^2 - 48 n + 128 =0
4 { n^2 - 12n + 32 } = 0
4 ( n -8 ) ( n-4) =0
n = 8 , 4
the number of terms == 4 , 8
therefore the A.P. is 22, 18 , 14, 10 , 6, 2 , -2 , -6
the sum of 4 terms = 64 & the sum of 8 terms is also = 64