Question

find the value of x for A.P. 1+6+11+16...... +x=148

Answer 1

Sn = n/2( 2a + (n-1)d)
148= n/2 (2×1 +(n-1)5
296 = n (2+5n-5)
296 = n (5n-3)
296 = 5n^2 - 3n
5n^2 -3n-296
5n^2-40n+37n -296
5n (n-8)+37 (n-8)
(n-8)(5n+37)
n-8
n=8

5n +37
5n= -37
n= (-37)/5