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That doesn't look like a linear equation, and assuming you are working with only real numbers, the domain and range of that function extends to $\infty$, and is not limited to $[-4,4]$.

It appears that Wolfram Alpha is giving you the solution of the values of $x$ when the function is positive. You can get that in Sage by using solve:

sage: solve(abs(x) - 4 > 0, x)
#0: solve_rat_ineq(ineq=abs(x)-4 > 0)
[[4 < x], [x < -4]]

That doesn't look like a linear equation, and assuming you are working with only real numbers, the domain and range of that function extends to $\infty$, and is not limited to $[-4,4]$.Whoops! Stupid answer deleted. :-/

sage: solve(abs(x) - 4 > 0, x)
#0: solve_rat_ineq(ineq=abs(x)-4 > 0)
[[4 < x], [x < -4]]