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Necessary and Sufficient Conditions of Senior High School Mathematics
Let's work out the range of x in inequality first, okay?

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!