# Thread: Simple problem with triangle

1. ## Simple problem with triangle

It's been many years since my geometry classes, but hoping someone will help me with this simple problem:

Say you have a triangle where side a is 76mm, and side b is .5mm. What is side b if side A were to be 700mm?

Is this a simple rule of 3 problem?

Thanks!

2. ## Re: Simple problem with triangle

Originally Posted by Kabibble
with this simple problem: Say you have a triangle where side a is 76mm, and side b is .5mm. What is side b if side A were to be 700mm? Is this a simple rule of 3 problem?
Perhaps you should tell us what the rule of three is?

As stated that are many possible answers.
Does $\displaystyle \angle A$ remain fixed? OR is this a similarity(proportionality) question?

In other words we need more details.

3. ## Re: Simple problem with triangle

The rule of three is basically a:b = c:d where if you know three of those numbers you can extrapolate the 4th.

In my situation the angle does not change.

4. ## Re: Simple problem with triangle

Then, WHY use a triangle?

a/b = c/k
a,b,c = givens; solve for k.

Btw, google "rule of three".
Your definition is from where?

5. ## Re: Simple problem with triangle

Interesting! I did google "rule of three" and got a page on the "rule of three writing". But there is also a page titled "rule or three math" which gives the definition kabibble gives. Admittedly, that is a Charles Dodgson (writing as "Louis Carrol"), in a book of (mostly mathematics) puzzles, refers to the "rule of three" repeatedly.

6. ## Re: Simple problem with triangle

By the way, Rule of three is also discussed here:

https://en.wikipedia.org/wiki/Cross-...#Rule_of_Three

7. ## Re: Simple problem with triangle

Originally Posted by HallsofIvy
Interesting! I did google "rule of three" and got a page on the "rule of three writing". But there is also a page titled "rule or three math" which gives the definition kabibble gives. Admittedly, that is a Charles Dodgson (writing as "Louis Carrol"), in a book of (mostly mathematics) puzzles, refers to the "rule of three" repeatedly.
The Reverend Mr. Dodgson probably taught this as university mathematics in 1860.
Here is a reasonable reference.