The lines
Question:

The lines $x+y=|a|$ and $a x-y=1$ intersect each other in the first quadrant. Then the set of all possible values of a is the interval:

1. (–1, 1]

2. $(0, \infty)$

3. $[1, \infty)$

4. $(-1, \infty)$

Correct Option: , 3

Solution: