AriM Group Title Using the quadratic function, provide the x intercepts of x^2+4x-21 Can someone just tell me what the quadratic function is..? one year ago one year ago

1. myininaya

The quadratic function you have is x^2+4x-21 The graph will be a parabola

2. myininaya

To find the x-intercepts, set your quadratic expression(function) equal to 0. Then solve for x.

3. AriM

hmm thats what i did @myininaya and i got x = -7 and 3 but the teacher wrote -2 and use quadratic function..

4. myininaya

What is -2 suppose to be ? Your x-intercepts are correct for this quadratic function.

5. AriM

Oh im just saying he took off 2 points and wrote use quadratic function.

6. myininaya

Does he mean formula?

7. myininaya

The quadratic formula is $x=\frac{-b \pm \sqrt{b^2-4ac}}{2a}$

8. AriM

hmm ill try it.

9. AriM

10. myininaya

Np. Good luck.

11. AriM

tnx

12. AriM

oh if you do the quadratic function you get 3 and -7. Can you check that for me? @myininaya

13. AriM

actually, never mind. I see his point but you could have just done (x+7) (x-3) and gotten the intercepts that way.

14. AriM

do you write it as (3,0) and (-7,0) though?

15. myininaya

Yep You could have factored or used the quadratic formula.

16. myininaya

It is more proper to say the x-intercepts are (3,0) and (-7,0) I would say it is informal to say they are 3 and -7

17. AriM

Yea, i understand.

18. myininaya

Coolness.