Question

The parabola y=x^2+3x-18 crosses the x-axis at

Answer 1

Solve the quadratic!

Answer 2

how do i do that

Answer 3

http://www.khanacademy.org/math/algebra/quadratics/v/solving-quadratic-equations-by-factoring-avi

Answer 4

its different how would i start my problem

Answer 5

Okay. Let me teach you in 2 minutes.

Answer 6

Consider this equation: ax^2 + bx + c

What we do, we look for TWO terms whom when we
MULTPLY, we get the value of a*c
And when we
ADD those same terms, we get the value of b!

Read this statement 3 times, try to understand. Tell me when we agree till here.

Answer 7

okay im good from here wats next

Answer 8

Alright! So in your case:
x^2+3x-18

a = 1, b = 3 and c = -18.

Agree?

Answer 9

yes

Answer 10

Okay. So:

a*c = 1*-18 = -18
AND
b = 3

So now we have find TWO terms (negative or positive), which when we
ADD we get 3 and when we MULTIPLY we get -18.

Agree?

Answer 11

yes

Answer 12

Perfect. Now start searching those terms.

+6 and -3.

Check: 6*-3 = -18 (a*c)
6 + (-3) = +3 (b)

Answer 13

Saifoo.Khan outstanding, Factoring gives (x+6)(x-3) =0. The product of 6*-3 = -18, their sum is +3. The roots are the negative of those factors.

Answer 14

can it be 3 and -6 as well

Answer 15

Yes. Since we get 2 roots, we rewrite as:

x^2 +6x - 3x - 18 =0

then make pairs,

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

Finally:

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

Answer 16

@jmays14 : No! It can't be!

6 - 3 = 3

-6 + 3 = -3

Answer 17

so that means the parabola doesnt cross the x axis

Answer 18

It does!
at
x = +3 and x = -6

Answer 19

okay these are the answer choices that i have but -6 and 3 isnt one

(A) 3 and -6
(B) 2 and -6
(C) 3 and -9
(D) 2 and -9
(E) The parabola does not cross the x-axis.

Answer 20

i mean 6,-3

Answer 21

It's A!

Answer 22

oh okay can u hlep me with 1 more please

Answer 23

Umm. Okay. Post it on left.