Question

what are the zeros of $f(x) = x^2 + x - 20?$
a. $x=-10$ and $x=2$
b. $x=-5$ and $x=4$
c. $x=-4$ and $x=5$
d. $x=-2$ and $x=10$

Explanation:

Step1: Set function to 0

$x^2 + x - 20 = 0$

Step2: Factor quadratic equation

Find two numbers that multiply to $-20$ and add to $1$: $5$ and $-4$.
$(x + 5)(x - 4) = 0$

Step3: Solve for x

Set each factor equal to 0:
$x + 5 = 0 \implies x = -5$
$x - 4 = 0 \implies x = 4$

Answer:

B. $x=-5$ and $x=4$