## andriod09 3 years ago Need help on Quadratic equations please! The equation is on the comments.

1. andriod09

$4x^{2}+9x=0$ i know that the answer is: $x=\frac{ -9\pm \sqrt{81-4(4)(2)} }{ 8 }$

2. gezimbasha

Much easier to solve your problem would be to factor out an x,$x(4x+9)=0$now you have two solutions,$x=0$and$4x+9=0$$4x=-9$$x=-\frac{9}{4}$and you get

3. imron07

The equation is correct. But you put innocent "2" instead of "0" for c.

4. andriod09

huh? the thing messed up, give me a sec

5. gezimbasha

Well, then you can do the following:$x_{1/2}=\frac{-9 \pm \sqrt{9^2-4*4*0}}{2*4}$simplifying that you get,$x_{1/2}=\frac{ -9 \pm 9 }{ 8 }$Compute the rest

6. andriod09

I have to use: $ax^{2}+bx+c=0$ and i have to use: $x=\frac{ -b\pm \sqrt{b^{2}-4ac} }{ 2a }$

7. gezimbasha

Yes.. that is what I have used. Just make c=0, and you will get the same result as I have.

8. andriod09

but c = 2... thats what the answer says.

9. gezimbasha

Well then you have given us a wrong problem$4x^2+9x=0$does not have a c in it..

10. andriod09

my bad... /facepalm its: $4x^{2}+9x+2=0$

11. andriod09

@gezimbasha

12. gezimbasha

Hehe, no worries. Now you have to use the formula you input$x_{1/2}=\frac{-9 \pm \sqrt{9^2-4*4*2}}{2*4}$compute the values inside the square root first$x_{1/2}=\frac{-9 \pm \sqrt{81- 32}}{8}$and complete calculation$x_{1/2}=\frac{-9 \pm 7}{8}$ and you get,$x_1= -2$$x_2=-\frac{1}{4}$

13. andriod09

where did you get $x _{1/2}$

14. gezimbasha

That just means that there are two solutions we will get from the equation. Its just mathematical notation. I am used to writing it like that. Don't worry, you can write just x, it will be fine.

15. andriod09

im only in high school. :/ :L

16. gezimbasha

Yeah I figured. The quadratic equations are studied extensively in high school. You're doing good tho. Might want to reconsider your profile picture heh ;)

17. andriod09

it says i don't hate math. open my profile and look at the white! everyone says that. lol do you not see the white scribble on the $^{don't}$ I hate math

18. gezimbasha

Oh.. then I owe you an apology. XD.

19. andriod09

Its okay. I need to make it bigger anyway. lol. Thanks tho.

20. gezimbasha

You're welcome man. Anytime!

21. andriod09

I gave you a medal. dont for get to give one back~ ;)

22. gezimbasha

Hey, my bad, my first day over here.

23. andriod09

what do you mean?

24. gezimbasha

This is my first day in open study, so I'm still getting used to the medals and stuff.

25. andriod09

how would i set up: $3x^{2}+11x+5=0$ and oh. i didn't know

26. gezimbasha

Same principle, replace a=3, b=11, and c=5.

27. andriod09

i mean in the fraction form