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 Post subject: Ahhh!!!! Algebra!!
PostPosted: Sun May 20, 2012 12:45 pm 
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Joined: Sun May 13, 2012 1:18 pm
Posts: 10
Hi,

My dd can't grasp alegbra and consequently is finding it hard to explain this=Area=1/2(a+b)H for the area of a trapezium.Could I please have a clear explanation....Thanks 8)


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 Post subject: Re: AHHH!!!!ALGEBRA!!
PostPosted: Sun May 20, 2012 12:53 pm 
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Joined: Tue Apr 10, 2012 4:24 pm
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i think uve to post this in maths forum isnt it. is that from VR? coz i havent come across such a qstn in VR. :?


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 Post subject: Re: AHHH!!!!ALGEBRA!!
PostPosted: Sun May 20, 2012 1:02 pm 
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This isn't algebra, it's area!

To find the area of a trapezium you find the average length of the parallel sides and then multiply by the perpendicular distance between them.


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 Post subject: Re: AHHH!!!!ALGEBRA!!
PostPosted: Sun May 20, 2012 1:07 pm 
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Joined: Tue Apr 10, 2012 4:24 pm
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Guest55 wrote:
This isn't algebra, it's area!

To find the area of a trapezium you find the average length of the parallel sides and then multiply by the perpendicular distance between them.



is this from VR? :?


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 Post subject: Re: AHHH!!!!ALGEBRA!!
PostPosted: Wed Jun 06, 2012 9:43 pm 
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Joined: Wed Jan 25, 2012 7:43 pm
Posts: 189
It is Geometry, not algebra :)

Formula given by both suttoncoldfield and Guest55 is of course correct.

Here is a derivation of the formula for trapezium's area.

Let us say we have a trapezium with two parallel sides (of lengths 'a' and 'b'), and a height of 'H'.

Draw a diagonal across the trapezium i.e. draw a line connecting two opposite vertices. Now, the trapezium looks like a combination of Two Triangles whose base lines are parallel to each other. These triangles have base lengths of 'a' and 'b', and both have the the same height of 'H'.

Area of Trapezium is therefore = Sum of Areas of the Two Triangles
= (aH)/2 + (bH)/2
= (a+b)H / 2

Derivation of Triangle's Area ( 1/2 x base x height) is of course a different story :)

Btw, I just noted this in wikipedia

Wikipedia wrote:
The word trapezium has several meanings:
(Outside the US) – a quadrilateral with one pair of parallel sides (a shape known in the US as a trapezoid).
(In the US) – a quadrilateral with no parallel sides (a shape known elsewhere as a general irregular quadrilateral).


Didn't know that a trapezium does not have parallel sides if it is on the other side of the pond. One learns something everyday :)


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 Post subject: Re: AHHH!!!!ALGEBRA!!
PostPosted: Wed Jun 06, 2012 11:36 pm 
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Joined: Sat Dec 17, 2011 12:02 pm
Posts: 102
Is this a question for eleven plus maths? :?


Last edited by BusyQueenBee on Mon Jul 09, 2012 9:00 pm, edited 1 time in total.

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 Post subject: Re: AHHH!!!!ALGEBRA!!
PostPosted: Sat Jun 09, 2012 11:19 pm 
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Location: Essex
I don't know about other areas and without digging out the paper I cannot remember whether the Essex CSSE Maths this time required such knowledge, but the formula is one of the two "you might need to use these" given at the beginning of the SATS Level 4-6 Maths papers.

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 Post subject: Re: AHHH!!!!ALGEBRA!!
PostPosted: Sun Jun 10, 2012 7:37 am 
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They are KS3 papers ... not appropriate for KS2 children as they are based on the KS3 'old' curriculum. They would not be used in KS3 now as they are not focused on the new style of questioning.


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 Post subject: Re: Ahhh!!!! Algebra!!
PostPosted: Mon Jun 25, 2012 10:35 am 
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Joined: Sat Jun 23, 2012 5:07 pm
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suttoncoldfield wrote:
Hi,

My dd can't grasp alegbra and consequently is finding it hard to explain this=Area=1/2(a+b)H for the area of a trapezium.Could I please have a clear explanation....Thanks 8)



Hi Not to worry mate and it is absolutely great to see dd has been challenged. Just think of 'area' as the space inside the shape and "Area=1/2(a+b)H" will make more sense if you draw a trapezium and label the two parallel length as "a and b" of your choice. All then is required to substitute the appropriate values and obtain a numerical answer.

However, if your dd is struggling with substitution then that's algebra and I would suggest dd should work on that before moving on to Areas which off-course can be done with using letters and just simply do the steps but I think using "Area=1/2(a+b)H" serves a great purpose in enhancing algebraic skills.

Any questions, please do not hesitate to contact.

Regards

AEC


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