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VCE Methods Question Thread!
b^3:
--- Quote from: tqn on December 08, 2011, 08:48:16 pm ---
--- Quote from: b^3 on December 08, 2011, 08:23:34 pm ---
--- Quote from: tqn on December 08, 2011, 08:00:07 pm ---Hi I have a question from the Essentials book:
The dimensions of an enclosure are shown. The perimeter of the enclosure is 160 m.
Find a rule for the area, A m^2, of the enclosure in terms of x.
Can someone please help me out? I can't seem to get it through my head :S
(the Image is in the form of an attachment as i don't know how to embed it into a post -_-")
--- End quote ---
Firstly find the perimeter in terms of x and y
perimeter = y+x+20+12+(y-20)+(x-12)
now that equals 160 m
2y+2x=160
so y=80-x
Now to find the area split it up into two shapes, lets split it the vertical way.
Area=(20)(x)+(y-20)(x-12)
Area=20x+(y-20)(x-12)
Now we know that y=80-x, so sub that in
Area=20x+(80-x-20)(x-12)
=x2+92x-720 m2
--- End quote ---
Ohhh I get it, I forgot to find y first then to sub it in ^^" Although, the answer I got was -x2 + 92x - 720 m2 so is there any difference with the x2 or... :S
Also thanks for the help as well :)
--- End quote ---
Yeh thats right, just missed the negative when I typed it out, had it written down right and copied it wrong.
tqn:
O ok then. Once again thanks very much for the assistance :)
Dominatorrr:
QUESTION ATTACHED
How do I find the values of a and b?
b^3:
--- Quote from: Dominatorrr on December 15, 2011, 08:30:58 pm ---QUESTION ATTACHED
How do I find the values of a and b?
--- End quote ---
This exact question has been on one of my SACS before. Anyway since the diameter at the top of the structure is 20m, you have the point 20/2=10 away from the origin and up 40m (height) i.e. the point (10,40). Now at the base you have a height of 0 and 50m from the origina so you have the point (50,0). Then plug those two points back into the equation to find a and b.
brightsky:
we know that the graph passes through these points:
(50,0), (-50,0), (10, 40), (-10,40)
so...subbing x and y coordinates:
0 = a/50^2 + b
40 = a/10^2 + b
0 = a + 2500b..[1]
4000= a +100b..[2]
[2]-[1]:
4000 = -2400 b
b = -5/3
so a = 2500*5/3 = 12500/3
hope these correlate to the answers, these numbers look weird.
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