Find the inequality of X≥3 or x ≤- 1/2.

According to x≥a is 2x &；; # 178; A necessary and sufficient condition for -5x-3≥0

That is, x≥a can be deduced as X≥3 or x ≤- 1/2.

Therefore, a≥3

If you can read the number axis and understand the range of values, then there is no problem!