Algebra question (many years out of school)?

Question

Hi, I graduated high school and uni with very high grades in math (over 10 yrs ago), and now I'm trying to solve a seemingly straightforward algebra equation and am unbelievably disappointed at how much I forgot.

Basically, I'm trying to solve x in this:

10000 = 0.075/x - x

so I had a hard time isolating X and decided to search online to see whet the heck i'm doing wrong. so i came across the quadratic equation:

ax^2 + bx + c = 0

which turns my equation into:

x^2 + 10000x - 0.075 = 0

That's supposed to make it easy to solve x using the quadratic formula:

x = (-b +/- sqrt(b^2 - 4ac)) / 2a

but i basically end up with the sqrt of 100000000.3, which is obviously the wrong answer.

The value of X SHOULD be roughly 810, it's just that the method of getting to it is unclear to me and is honestly driving me up the wall.

Thanks a million for whomever can help!!

Answer 1

Hi,

You (along with everyone else) are doing this correctly, but maybe the trouble is the way you set up your equation. I suspect that since you know the answer, either you have a problem which you have set up the equation for, and know about what the outcome should be, or someone told you the answer, and they've done the problem incorrectly.

I suggest that if it's the former, you post the reason you're trying to solve this equation, and maybe we can help you set it up. If it's the latter, I'd find some new study partners...

Hope that helps,
Matt

Answer 2

Parentheses would have helped.

I presume you mean

10000 = (0.075/x) - x

Multiplying by x gives what you said:

x^2 + 10000x - .075 = 0

Obviously, the answer is not around 810. 810 squared and 10000 * 810 are both positive and cannot add to zero.

x has to be an extremely tiny number, so tiny that we can ignore x^2 for now. That gives us

10000x = .075
x = .075/10000 = 7.5 * 10^-6

x^2 is thus around 50 * 10^-12 and can truly be ignored.

Oops, forgot that x could also be a negative number of substantial absolute value. In that case, we can ignore the .075 and get

x^2 = -10000x
x = -10000

Crazy Horse and Meekaboox have it all correct and concise, but then Meekaboox gets distracted and notices with a "hmmmmm" and a "wow" that something has gotten "hard." Hey, Meekaboox, keep your mind on the answers and your hand out of your pants.

Answer 3

x^2 + 10000x - 0.075 = 0

you need to put this into 2 brackets

so u will av
(x- _)(x+_) and findin 2 numbers that add up to -0.075 and multyiply to give is hard so ye u wuld av to go to

-b +/- sqrt (b^2 - 4ac) all over 2a

so a is 1
b is 10000
c is 0.075

so if u used - your x would be -9999.999993

and if you used + your x would be -7.5 x 10 ^ -06

hmmmm wow this is hard....

i duno sorry :(

Answer 4

You're actually doing the right thing. You get two solutions for x, one is about 10000, the other is about -10000. If you substitute these into the original question, you'll see that the negative answer solves the equation.

As for the answer being about 810; this does not even come close if you put it in.

See, you already had the right answer - you didn't have to even come on here!

Answer 5

The first person to answer was correct in saying that you had it right with:

x^2 + 10000x - 0.075 = 0

Using the quadratic equation:
x1 = 0.000007499999810534064
x2 = -9999.999992500001

Both of these answers work. I hope this helps, but you had pretty much answered your own question, you just wasn't expecting the answer that you got!

Answer 6

Wow, you're the sensible one. eighth grade and already taking Algebra 2? in any case, i replaced into less than the effect that Algebra 2 commonly is going on to Precalc, a minimum of that is the way it replaced into back contained in the day even as i replaced into in severe college. What precisely is college Algebra? feels like it overlaps with Algebra 2? i'd listen on your counselor in spite of the actuality that, no experience in taking the opportunity of probably ruining your freshman GPA fantastically if there is no hurry. I took Precalc in my junior 3 hundred and sixty 5 days and that i already concept i replaced into less than an speeded up software!

Answer 7

10000 = 0.075/x - x multiply by x
10,000x=.075-x^2 add x^2-.075 to each side
x^2+10000x-.075=0

x=(-10000+/-√(10,000^2+4*.075))/2
x=-5000+/-√(100,000,003) /2
x=7.5*10^-5
x=-10,000.000075

Answer 8

did you mean .075/(x-x) or (0.075/x) - x?