A number line graph includes the points at real numbers \(a\) and \(b\), as shown below. Which of the following inequalities expresses an interval that must include the product \(ab\) ?

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We can use test values, such as \(a=-\dfrac{3}{4}\) and \(b=\dfrac{1}{2}\):

$$ ab = -\frac{3}{4}\cdot \frac{1}{2} $$ $$ = -\frac{3}{8} $$

This fits only the second option.