If $AB = 0$, what must be true about $A$ or $B$? Use this idea with $x^2 - 9$ and $3x + 5$.

After you set each factor equal to zero, solve $x^2 - 9 = 0$ and $3x + 5 = 0$. Then compare all the values you find to the four answer choices.

In Desmos, type y = (x^2 - 9)(3x + 5) to graph the function corresponding to the left side of the equation.

Look for the points where the graph crosses the x-axis (where $y = 0$). Tap each intercept to see its x-coordinate; these x-values are the solutions to the equation.

Compare the x-coordinates of the intercepts you see in Desmos with the four options. Select the choice that matches one of those x-values.

The equation is

If a product of two expressions equals zero, then at least one of the factors must be zero. So set each factor equal to zero:

• $x^2 - 9 = 0$
• $3x + 5 = 0$

Solve the first factor:

So this factor gives two possible solutions: $x = 3$ and $x = -3$.

Solve the second factor:

So this factor gives another possible solution: $x = -\frac{5}{3}$.

All solutions of the equation are $x = 3$, $x = -3$, and $x = -\frac{5}{3}$.

Check the answer choices:

• $-\frac{3}{5}$ is not one of these.
• $\frac{5}{3}$ is not one of these.
• $5$ is not one of these.
• $-\frac{5}{3}$ is one of these.

So the correct answer is $-\frac{5}{3}$.