Need help with my geometry

[prichard]

I think your original assumption that the slight different of the one side at 6" shorter doesn't matter is correct. You'll end up with a little extra concrete is anything, not short.

I can draw it in CAD to be sure but I'm not going to start figuring the math on the lopsided polygon. There is really only one way to draw and measure that with the dimensions you provided so it can be calculated with what's there whether you know the angles or not.

 

[tallyho8]

Are those angles at the top = ... and what value ?

The top angles are equal but I don't know the degree. Is that imperative?

 

[prichard]

According to CAD it is 432.56' sq ft

 

[tallyho8]

Next question. In the future will schools even teach geometry or will things like CAD classes replace those classes?

 

[Dapolksjj]

It's been so long since I got out of school, I can't remember how to solve this problem. I can't even remember if its geometry, trigonometry or whatever. Maybe its early Alzheimer's? Please help me find out how many square feet this is. <img src="http://www.tractorbynet.com/forums/attachment.php?attachmentid=465525"/>

I finally got my math right. The undetermined leg in the triangles is 18'. The areas of the two triangles is 90 sqft respectively. The area of the rectangle is 180sqft. Total area is 360sqft. Area of triangle is .5(18x10). a squared + b squared = c squared computes the unknown leg.

 

[LD1]

LD1, I just posted a fairly easy question (that I didn't know the answer to) without complete details of angles, exact lengths, etc. because I just needed to know how much concrete to order and I always order at least 1/2 a yard extra so I didn't need an exact answer and I did not supply exact details because I did not think it would really matter. Most people would assume that the top and bottom lines were parallel from my original drawing and give me a close enough answer for my question, which they did.

Now you say you did not answer earlier because you did not want to assume that the lines were parallel until I revealed that it was for a driveway apron and then you "assumed" that they were parallel.

Well, so much for assuming. They actually are not parallel and the 2 sides are different lengths though I did not disclose this earlier because I did not want to over-complicate the matter and I had another part also that was a rectangle of 8' X 10' that I was easily able to figure was 80 sq. ft. that I added on to your correct answers without disclosing.

Now if any of you wish to tell me the exact measurement of my apron from the enclosed drawing, with more details, and the amount of concrete I should order, adding 1/2 yard extra, to be safe, please do so. I will see how much it varies from the 10 1/2 yards I am planning to order.

PS: The concrete is 6" thick.

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I didnt answer earlier because I didnt see the post until after you already revealed it was for an apron. I said I "wouldnt have answered" without further info.

Yes the question was easy if we had known from the start that it didnt need to be an exact as it was for a concrete apron. But for all we know you could have been machining a precision part for something, or who knows what else. Without knowing the level of exactness needed, hard to answer based on you first post only.

 

[prichard]

The top angles are equal but I don't know the degree. Is that imperative?

No. There is only one possible area enclosed by a 4 sided polygon with those dimensions.

Next question. In the future will schools even teach geometry or will things like CAD classes replace those classes?

CAD is much harder to teach than geometry but it's likely they'll just hand out formulas or apps for phones to do this stuff and not teach anything.
I did study, enjoy and do well in geometry but have used so little of it in the last 30 years. Like your drawing on paper using CAD lets me know I'm right rather than counting on those old brain cells that are still limping along. My CAD brain cells are much fresher than my geometry brain cells.

 

[LD1]

I finally got my math right. The undetermined leg in the triangles is 18'. The areas of the two triangles is 90 sqft respectively. The area of the rectangle is 180sqft. Total area is 360sqft. Area of triangle is .5(18x10). a squared + b squared = c squared computes the unknown leg.

360 is still way off. Where are you getting 18' from?

 

[Dapolksjj]

It's been so long since I got out of school, I can't remember how to solve this problem. I can't even remember if its geometry, trigonometry or whatever. Maybe its early Alzheimer's? Please help me find out how many square feet this is. <img src="http://www.tractorbynet.com/forums/attachment.php?attachmentid=465525"/>

it's time to go back to school for me! My last calculation was wrong! The unknown leg in the triangle is 22'.the area of the figure is 440 sqft. Sorry about that!

 

[SPYDERLK]

The top angles are equal but I don't know the degree. Is that imperative?

For an exact answer, yes. But for practical purposes you have increased the area by ~ 78sq-ft