Register to reply 
Area as a function of x: A(x)=2xh. Where did the 2 come from? 
Share this thread: 
#1
Dec712, 12:21 PM

P: 5

This came from a friend of mine who has a math book on hand with a statement that doesn't seem to make sense. Neither of us are in school/college at the moment. This is math for the fun of it.
I tested out A(x) = xh by itself and substituted h by making it relative to x (x/2 = h or that is to say that the height is 1/2 the width). When looked at it that way, the output for A(x) makes sense for the area. I cannot make sense of the 2 though in A(x) = 2xh. So the question of the hour is as stated above. Where did the 2 come from? 


#3
Dec712, 01:07 PM

Mentor
P: 21,305

You might be misreading the information in the problem. If half the length is x, then the length is 2x, and then area would then be A = 2xh. 


#4
Dec912, 11:36 AM

P: 362

Area as a function of x: A(x)=2xh. Where did the 2 come from?
Most like we're dealing with a function like y=3, when the author saids "area, he is probably referring to a rectangle extending equally on either side of the origin, hence A=2xh, since x is only half the extension.



#5
Dec912, 12:17 PM

Sci Advisor
HW Helper
PF Gold
P: 12,016

just a guess:
You have two sides, the overside and the underside, of the rectangular plot, each with area x*h 


#6
Dec912, 12:31 PM

P: 166

This is from the CK12 Trig book.



#7
Dec912, 01:23 PM

Mentor
P: 21,305

I can begin to follow what they're doing, but then what you have here makes no sense. We have 100 ft of fencing that will be used to fence in three sides of a rectangle. From one equation they give  x + 2h = 100  we can conclude that the side parallel to the barn has length x (ft) and the two sides perpendicular to barn each have length h (ft). Skipping down to the end, you have x + 2ft = 100  that should be x + 2h = 100 So 2h = 100  x  this is OK Then you have h = 50   this is wrong Next you have A(x) = 2xh = 2x^50 ) and then A(x) = 100xJt 2 Neither of these makes any sense. 


#8
Dec912, 01:30 PM

P: 166

Don't shoot the messenger..
I copied it from here: http://archive.org/stream/ostmathc...metry_djvu.txt Didn't make any sense to me either. 


#9
Dec912, 02:13 PM

PF Gold
P: 6,340

If it was cut and paste, then why would you interpret the answer provided as "shooting the messenger"? Since the response was "if you have copied it correctly then the book is messed up". Why not respond, "thanks for confirming for me that the book is messed up" 


#10
Dec912, 02:17 PM

P: 166

[QUOTE=phinds;4190721]Copied as in "cut and paste"? (I'm not going to look through that whole thing to find what you are referencing.
You don't have to read the whole thing. CTRLF, "A(x)" will take you right to it. I copied and pasted. The source I copied from may be flawed somehow. 


#11
Dec1012, 02:14 AM

P: 5

Thank you all for your efforts. I too found that example of the fence in a different website full of examples. My friend had the very same example out of her book that she tried to work. I also saw how you cannot have an answer of 50 for x since that means you have 50 on one side and the other and a big, open hole going out into the open.
Check Example 6 in the link below: http://en.wikibooks.org/wiki/High_Sc...Lesson_Summary This does appear to be flawed. If several brains like us can collaborate and see some fault here, then perhaps we are right. I can always bring it up to someone tomorrow at the college nearby and see what the math lab has to say about it. 


#12
Dec1012, 02:40 AM

HW Helper
P: 2,952




#13
Dec1012, 06:14 AM

Sci Advisor
HW Helper
PF Gold
P: 12,016

If they are lichenproducers, it might actually work. 


#14
Dec1012, 06:51 AM

P: 181




Register to reply 
Related Discussions  
Window area question, express as function of Area  Precalculus Mathematics Homework  7  
Area of a Polar Function  Calculus & Beyond Homework  3  
Area as a function  Precalculus Mathematics Homework  4  
Area of a polar function  Calculus & Beyond Homework  0  
Express Area as a function of r  Precalculus Mathematics Homework  12 