Q. 15 A3.7( 6 Votes )

Solve for x1 + 6+11 + 16 +...+x= 148

Here, a = 1, d = 6 – 1 = 5 and Sn = 148

296 = n[5n – 3]

5n2 – 3n – 296 = 0

5n2 – 40n + 37n – 296 = 0

5n(n – 8) + 37(n – 8) = 0

(5n + 37)(n – 8) = 0

5n + 37 = 0 or n – 8 = 0

or n = 8

But is not a positive integer.

n = 8

x = a8 = a + 7d = 1 + 7 × 5 = 1 + 35 = 36

Hence, x = 36

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