Question

What is one possible value of x in this equation x^2-3x-18=0

Answer 1

Either -3 or 6.

You can write this equation as a function, then factor it. You can use the zero-factor rule (I think that’s what it’s called) to find the x-intercepts of the function, where the equation is equal to zero.

y=x^2-3x-18

Factor by grouping;
y=x^2+3x-6x-18
y=x(x+3)-6(x+3)
y=(x+3)(x-6)

When y=0, (x+3)=0 or (x-6)=0
x+3=0 when x=-3, and x-6=0 when x=6

Your possible values of x are -3 and 6.

Answer 2

x=6,-3

Explanation:

x²-3x-18=0

Find two numbers that multiply to get -18, and add to get -3!

(These two numbers are -6 and 3)

Now write them in an equation:

(x-6)(x+3)=0

Set both equations equal to 0:

A) x-6=0

B) x-3=0

2A) x=6

2B) x=-3