# Math Equation question **URL:** \ **Category:** Factual Questions\ **Created:** [February 7, 2001, 2:53am UTC](https://boards.straightdope.com/t/math-equation-question/53439 "2001-02-07T02:53:01Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![mongrel\_8](https://avatars.discourse-cdn.com/v4/letter/m/e274bd/32.png) [@mongrel\_8](https://boards.straightdope.com/u/mongrel_8)\ **Post date:** [February 7, 2001, 2:53am UTC](https://boards.straightdope.com/t/math-equation-question/53439/1 "2001-02-07T02:53:01Z")
I was wondering about something today and my calculus teacher didn’t help much so I decided that this was the best place to ask. What would the equation be for a function that would go through the points: [1,1], [2,.5], [3,.25], [4,.125], and so on so that for every increase of one in the x direction the y value halves itself from the previous time. I figured that it would have to be a logarithm graph or a hyperbola but I could figure out the equation. Any help? ---
**Author:** ![mongrel\_8](https://avatars.discourse-cdn.com/v4/letter/m/e274bd/32.png) [@mongrel\_8](https://boards.straightdope.com/u/mongrel_8)\ **Post date:** [February 7, 2001, 2:55am UTC](https://boards.straightdope.com/t/math-equation-question/53439/2 "2001-02-07T02:55:12Z")
Sorry, that was supposed to read “I could not figure out the equation or graph”. ---
**Author:** ![KarlGauss](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/karlgauss/32/3713_2.png) [@KarlGauss](https://boards.straightdope.com/u/KarlGauss)\ **Post date:** [February 7, 2001, 3:05am UTC](https://boards.straightdope.com/t/math-equation-question/53439/3 "2001-02-07T03:05:12Z")
y = 5[sup](x - 1)[/sup] ? ---
**Author:** ![RyanD004](https://avatars.discourse-cdn.com/v4/letter/r/848f3c/32.png) [@RyanD004](https://boards.straightdope.com/u/RyanD004)\ **Post date:** [February 7, 2001, 3:06am UTC](https://boards.straightdope.com/t/math-equation-question/53439/4 "2001-02-07T03:06:00Z")
well…i figure it’s the same as : x + a = y \* (1/2)^a if thats any help. I’m not in a good thinking mood tonightmand the only was i can think of is with a third variable. Hmm… youk now that there is a vertical asymtote(sp) at 0. I know a vertical asymtote means the function is undefined at x= 0… which means there an x in the denominator of something. I guess some math wizard will figure it out for you. ---
**Author:** ![RyanD004](https://avatars.discourse-cdn.com/v4/letter/r/848f3c/32.png) [@RyanD004](https://boards.straightdope.com/u/RyanD004)\ **Post date:** [February 7, 2001, 3:09am UTC](https://boards.straightdope.com/t/math-equation-question/53439/5 "2001-02-07T03:09:40Z")
You know, I would almost have sounded half-intelligent if i had taken the time to proof-read my post before I sent it in. ---
**Author:** ![Lance\_Turbo](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lance_turbo/32/6156_2.png) [@Lance\_Turbo](https://boards.straightdope.com/u/Lance_Turbo)\ **Post date:** [February 7, 2001, 3:09am UTC](https://boards.straightdope.com/t/math-equation-question/53439/6 "2001-02-07T03:09:48Z")
> [@](#): > > \*Originally posted by KarlGauss \* > \*\*y = 5[sup](x - 1)[/sup] ? \*\* I think you mean y = 2[sup](x - 1)[/sup] ---
**Author:** ![brad\_d](https://avatars.discourse-cdn.com/v4/letter/b/50afbb/32.png) [@brad\_d](https://boards.straightdope.com/u/brad_d)\ **Post date:** [February 7, 2001, 3:11am UTC](https://boards.straightdope.com/t/math-equation-question/53439/7 "2001-02-07T03:11:56Z")
I believe y = 2[sup]-(x-1)[/sup] fits those data points. x=1; y = 2[sup]0[/sup] = 1 x=2; y = 2[sup]-1[/sup] = 1/2 = 0.5 x=3; y = [sup]-2[/sup] = 1/4 = 0.25 x=4; y = [sup]-3[/sup] = 1/8 = 0.125 etc… ---
**Author:** ![jcgmoi](https://avatars.discourse-cdn.com/v4/letter/j/a9adbd/32.png) [@jcgmoi](https://boards.straightdope.com/u/jcgmoi)\ **Post date:** [February 7, 2001, 3:12am UTC](https://boards.straightdope.com/t/math-equation-question/53439/8 "2001-02-07T03:12:32Z")
y = 2sup[/sup] would fit your data set. ---
**Author:** ![KarlGauss](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/karlgauss/32/3713_2.png) [@KarlGauss](https://boards.straightdope.com/u/KarlGauss)\ **Post date:** [February 7, 2001, 3:17am UTC](https://boards.straightdope.com/t/math-equation-question/53439/9 "2001-02-07T03:17:58Z")
I honestly didn’t see the decimal points in the range. (Now it’s my eyesight, what will fail next?! :() ---
**Author:** ![Lance\_Turbo](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lance_turbo/32/6156_2.png) [@Lance\_Turbo](https://boards.straightdope.com/u/Lance_Turbo)\ **Post date:** [February 7, 2001, 8:36am UTC](https://boards.straightdope.com/t/math-equation-question/53439/10 "2001-02-07T08:36:44Z")
And I honestly can’t believe that I made a sign error in my attempted correction of you.