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VCE Stuff => VCE Mathematics => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Mathematical Methods CAS => Topic started by: nbalakers24 on February 12, 2010, 11:16:03 pm

Title: Methods - Help
Post by: nbalakers24 on February 12, 2010, 11:16:03 pm: Hi

I need help on this question:

(http://i47.tinypic.com/28cjdx3.jpg)

Help appreciated ! Thanks!

:D :D :D
Title: Re: Methods - Help
Post by: /0 on February 12, 2010, 11:34:43 pm: a) Split the figure up into 2 squares: $A = x \cdot 20 + (y-20) \cdot (x-12)=xy-12x+240$

The perimeter is $2x+2y = 160$ , giving us $x+y=80$ . Solving for y we can sub 'y' out of the Area equation so we are left with x.

b) For a start, we require $x > 0$ and $y>0$ , as lengths must be positive. Secondly we require that $x>12$ and $y > 20$ for the diagram to make sense. (Since these second restrictions are tighter than the first, we can ignore the first restrictions). These establish our lower bounds.

We can establish upper bounds from the perimeter equation $x+y=80$ .
Since $20<y$ , we have $x+20 < x+y = 80$ , so $x < 60$ .
Since $12<x$ , we have $12+y < x + y = 80$ , so $y < 68$ .

Thus, $x \in (12,60)$ , $y \in (20,68)$ .

c) It's a quadratic in the interval (12,60). Remember to leave open endpoints.

d) Find the turning point by completing the square or calculus.
Title: Re: Methods - Help
Post by: nbalakers24 on February 12, 2010, 11:37:54 pm: thank-you!

:D
Title: Re: Methods - Help
Post by: Aqualim on February 13, 2010, 03:18:42 pm: Quote from: /0 on February 12, 2010, 11:34:43 pm
a) Split the figure up into 2 squares: $A = x \cdot 20 + (y-20) \cdot (x-12)=xy-12x+240$

shouldn't it equal $xy-12y+240$ ?
Title: Re: Methods - Help
Post by: /0 on February 13, 2010, 10:34:19 pm: Quote from: Aqualim on February 13, 2010, 03:18:42 pm
Quote from: /0 on February 12, 2010, 11:34:43 pm
a) Split the figure up into 2 squares: $A = x \cdot 20 + (y-20) \cdot (x-12)=xy-12x+240$

shouldn't it equal $xy-12y+240$ ?

indeed
Title: Re: Methods - Help
Post by: samiira on February 14, 2010, 02:33:00 pm: hey.. how did u paste the picture there..??
Title: Re: Methods - Help
Post by: GerrySly on February 14, 2010, 02:34:19 pm: Quote from: samiira on February 14, 2010, 02:33:00 pm
hey.. how did u paste the picture there..??
Use the img tags

Code: [Select]
[img]http://url.to/image/here[/img]
Then just upload it to some photo hosting site like Photobucket or Imageshack
Title: Re: Methods - Help
Post by: samiira on February 14, 2010, 03:33:42 pm: ok.. kool.. thanks