3-4-5 Rule

Darren Wright

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Just something Dad taught me and I use from time to time on projects, like building decks, laying out walls, or squaring up outside projects. I thought maybe some of you may not have ever heard of it or been exposed to it. The 3-4-5 rule is used to get things laid out square at a 90 degrees.

How it works, is you measure out from the inside or outside corner in one direction and make a mark at 3', then measure out from the same corner the other direction 4'. Now measure from the 3' mark to the 4' mark moving one side in or out until the distance between the marks is 5' exactly, this will be 90 degrees.
square-joists-00-x.gif
You can increase the accuracy for larger projects by multiplying the figures in the rule (i.e. 3-4-5 x 2 = 6-8-10 or 3-4-5 x 3 = 9-12-15). Also it doesn't have to be feet, use inches or centimeters, or even yards if you've got a tape long enough. The math guys call this Pythagoras' theorem.
 
This rule was derived from Pythagorean's Theory for right (90°) triangles whereby the hypotenuse squared = the sum of each of the other two legs squares, i.e. C[SUP]2[/SUP]=A[SUP]2[/SUP]+B[SUP]2. As Darren pointed out, this is a handy way to set up, or confirm, a square corner for many applications.[/SUP]
 
This rule was derived from Pythagorean's Theory for right (90°) triangles whereby the hypotenuse squared = the sum of each of the other two legs squares, i.e. C[SUP]2[/SUP]=A[SUP]2[/SUP]+B[SUP]2. As Darren pointed out, this is a handy way to set up, or confirm, a square corner for many applications.[/SUP]

?HUH?????
 
Just something Dad taught me and I use from time to time on projects, like building decks, laying out walls, or squaring up outside projects. I thought maybe some of you may not have ever heard of it or been exposed to it. The 3-4-5 rule is used to get things laid out square at a 90 degrees.

How it works, is you measure out from the inside or outside corner in one direction and make a mark at 3', then measure out from the same corner the other direction 4'. Now measure from the 3' mark to the 4' mark moving one side in or out until the distance between the marks is 5' exactly, this will be 90 degrees.
View attachment 74628
You can increase the accuracy for larger projects by multiplying the figures in the rule (i.e. 3-4-5 x 2 = 6-8-10 or 3-4-5 x 3 = 9-12-15). Also it doesn't have to be feet, use inches or centimeters, or even yards if you've got a tape long enough. The math guys call this Pythagoras' theorem.

I think that is the one thing I actually use from tenth grade geometry.:D

Ike
 
?HUH?????

It's math talk Jon. Here, I'll translate:

Put a mark over here at 3 feet. Put another mark over yonder at 4 feet. When you move the two marks 5 feet away from each other, it's 90 degrees outside and it's getting too danged hot to work, so you go get a tall glass of lemonade and think of taking the family to the zoo to go look at all the animals. You know, the giraffes, lions, the square hippopotenuses, and so on. It's all pretty simple. :D
 
It's math talk Jon. Here, I'll translate:

Put a mark over here at 3 feet. Put another mark over yonder at 4 feet. When you move the two marks 5 feet away from each other, it's 90 degrees outside and it's getting too danged hot to work, so you go get a tall glass of lemonade and think of taking the family to the zoo to go look at all the animals. You know, the giraffes, lions, the square hippopotenuses, and so on. It's all pretty simple. :D

I was following along with the marks over yonder, but the concept of people paying to see animals???????? Why would someone do that????
 
I was following along with the marks over yonder, but the concept of people paying to see animals???????? Why would someone do that????

Who says you have to pay? Long story, but back in my misspent youth, a buddy and I found a place where we could climb over the fence unseen and get into the San Diego zoo for free. Did it several times that week. :whistling:
 
There are three pregnant indian women. One sleeps on a bear skin, one on a buffalo skin and one on a hippopotamus skin. The one on the bear skin has a boy. The one on the buffalo skin has a boy. The one on the hippo skin has twin boys. Therefore...........................the sons of the squaw of the hippopotamus is equal to the sons of the squaws of the other two hides.
 
Yeah Darren if only all school math had that value in use. Got to be right up there with 1+1 =2 in books of value in use. :)
Now if some one could really explain those crazy transmission line theory formulas I had to learn, which fabricated terms like Hype cosh.
Boy if ever there was A waste of my life it was that subject.


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I keep a couple of math books from college around, but using them less and less with finding calculators on the web. One of the books was from my "Technical" Math class. The instructor combined math, geometry, and calculus all in the same class. But rather than teaching theory and mind numbing formulas, he gave real-world examples of their uses, which made more sense to me. Still reference that book quite a bit.
 
I keep a couple of math books from college around, but using them less and less with finding calculators on the web. One of the books was from my "Technical" Math class. The instructor combined math, geometry, and calculus all in the same class. But rather than teaching theory and mind numbing formulas, he gave real-world examples of their uses, which made more sense to me. Still reference that book quite a bit.

I consider myself almost mathematically illiterate. Factor an algebraic equation? I have no idea. I can't tell a cosine from a street sign. But give me a practical application for that math and show me how to do the calcs, and I'm all over it. I've had a number of jobs that used a lot of math and had no problem with it as long as it was real-world stuff and not theories.
 
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