## anonymous one year ago -2x² - 7 = 4x Where are a, b, and c in this equation? How do I solve this with the quadratic equation?

1. Jamierox4ev3r

remember, a standard quadratic equation is always in this form: $$a^{2}x+bx+c$$ so you're going to need to manipulate this equation to set it to this formula

2. anonymous

Is a 2? Is b 4? Is C 7?

3. butterflydreamer

we have this equation: -2x² - 7 = 4x We need to rearrange it so that the x² part is positive. Therefore take the "-2x² - 7" to the other side of the equals sign and we get: -2x² - 7 = 4x 0 = 2x² + 4x +7 Standard form is : ax² + bx + c = 0 Therefore match it up with your equation and we get: a = 2, b = 4 , c = 7 Which you said.. so you're correct ^_^!

4. anonymous

How do I solve this?

5. anonymous

use this formula$x=\frac{ -b \pm \sqrt{b^2-4ac} }{ 2a }$

6. butterflydreamer

yeah use the quadratic formula (as stated by surjithayer) to solve for x :)

7. anonymous

1.58?

8. butterflydreamer

not quite we know a = 2, b = 4 and c = 7 plug these values into the quadratic formula: |dw:1433428335720:dw|

9. butterflydreamer

note: we cannot square root a negative number. Therefore, there will be no solution... What i mean by this is that in this part here: |dw:1433428482052:dw| And we can't square root -40. Therefore x will have no solution

10. anonymous

WHAT?!

11. anonymous

I thought that when the numerator says "$\pm$", you were supposed to change the number to a positive whenever you square rooted it.

12. butterflydreamer

hmm.. the plus and minus sign, means that you can get TWO solutions... for x. You want to concentrate on what is happening INSIDE the square root sign: |dw:1433430575846:dw| plug it into the calculator and tell me if you get an answer :)

13. butterflydreamer

you should get a math error. Why? Because we can't square root a negative number.