$\displaystyle 7=\frac{1}{2}|4x| -1 $ or $\displaystyle -7=\frac{1}{2} |4x| -1$
I tried solving the second one but didn't get it...Please Help!!!
"The second one"? Do you mean $\displaystyle -7= \frac{1}{2}|4x|- 1$?
There is no reason why you should! The problem is to solve f(x)= 7, not f(x)= -7.
(And, in fact, since it leads to $\displaystyle \frac{1}{2}|4x|= -6$, there is no x satisfying that equation.)