Let, ax+by+c=0 be a variable straight line, where, a, b, c are `1^(st),3^(rd)` and `7^(th)` terms of an increasing AP, then the variable straight line always pases through a fixed point, whose abscissa is:

Explanation

Let .d. be the common difference of AP, then b=a+2d and C=a+6d
`therefore(b-a)^3=c-a` `implies2a-3b+c=0`
`therefore` The variable straight line passes through (2,-3).
`therefore` The abscissa = 2