Question

how do i solve y=x^2-4x-45 to find all x intercepts

Answer 1

Factor!

Answer 2

How do you do that? can you help?

Answer 3

Well you want to make it into (x+a)(x+b) form

Answer 4

so when you remultiply it it gives you x^2+ax+bx+ab

Answer 5

what are some values of a and b that could give you ab=-45?

Answer 6

9 and 5

Answer 7

right, note that one of them needs to be negative.
Now how would you make ax+bx = -4x from your 9 and 5?

Answer 8

-5

Answer 9

is the answer possibly 5 and -9?

Answer 10

why yes it is. so what does your y=(x+a)(x+b) become?

Answer 11

(x-5) and (x+9)

Answer 12

you have your a and b values backwards actually.
when you multiply (x-5)(x+9) = x^2+4x-45

Answer 13

so its -9 and +5?

Answer 14

yes those are your a and b values.
Next you need to find values of x to provide 0=(x-9)(x+5)
those will be when your y=0

Answer 15

NO WAIT -5 and 9