## kevin8374 3 years ago solve for r r^2+3r=8 Example r^2+3r=1 r=-3+√13/2,-3-√13/2

1. philips13

looks like the quadratic equation might help here

2. brinethery

r^2 +3r -8 =0 a=1 b=3 c=-8 Use the quadratic formula to get your answer(s) for x.

3. kevin8374

The quadratic equation is where my problem lies

4. brinethery

Do you know what the quadratic formula is?

5. brinethery
6. brinethery

((-1) +/- sqrt ((3)^2-(4)(1)(-8)))/((2)(1))

7. brinethery

(-1 +/- sqrt (41))/2 ***THAT MEANS*** x = (-1 + sqrt(41))/2 x = (-1 - sqrt(41))/2

8. kevin8374

Thanks so much

9. brinethery

This is what you do whenever factoring is impossible.

10. brinethery

Or if you're too lazy to factor :-)... like I usually am LOL

11. kevin8374

so how would i put x^2+7x=10 into the quadratic equation

12. brinethery

Okay so your format is going to be ax^2+bx+c So with x^2+7x=10, you always always always get everything on the left side. You're setting it equal to zero. x^2+7x-10=0 Now what are a, b, and c?

13. kevin8374

sorry typed problem wrong x^2+7x-10=0

14. brinethery

k... so what do you think a, b, and c are?

15. kevin8374

a is 1 b is 7 c is 10

16. brinethery

Yup!

17. brinethery

I'll ask you one now. -x^2+2x+3 What is "a" in this case?

18. kevin8374

-1

19. brinethery

yep

20. kevin8374

my problem is keeping it all in order

21. brinethery

Now if there's a term, say b=-2 and you need to plug it into your formula, the first thing you're putting in is -b. So how to do that: -(-2). So that will be a +2.

22. brinethery

I understand. And I would recommend to do the problem in as many steps as you need to. And to slow down and pay close attention. I took an engineering problems course last quarter and I made a lot of mistakes when I didn't pay attention :-)

23. brinethery

You can try that problem and we'll compare answers if you want.

24. kevin8374

ok is it -7+√89/2,-7-√89/2

25. brinethery

That's what I got too. You know what you're doing!

26. kevin8374

You have no idea how much you have helped me thanks again!!!!!

27. brinethery

I'm glad :-) So step 1: Get everything on the left side so that it's set equal to zero. step 2: write down what your a, b, and c values are step 3: plug in to the formula and go slow

28. kevin8374

I truly cannot thank you enough I have been struggling for days

29. brinethery

I would recommend Paul's online notes as an alternative to your book. Most algebra books truly suck. http://tutorial.math.lamar.edu/Classes/Alg/SolveQuadraticEqnsII.aspx