I'm confused why this was seperated from the original thread...? I don't know where the other half of the post went. I've done the question with the diagram I just wanted it checking. This makes even less sense without the context of the original thread (especially with the other questions I posted). It's probably best just deleting this thread or both of them and starting again.
Denis said:
Monk, very badly worded: perimeter ABCDE = 65 means what?
I see you used AB+BC+CD+DE = 65 to get x+y = 25:
but that's not a perimeter.
The perimeter of figure ABCDE includes diagonal AE;
a perimeter refers to a fully enclosed diagram.
Main Entry: pe·rim·e·ter
Function: noun
1 a: the boundary of a closed plane figure
Thanks for the reply. I didn't post all my working, some of it was in the other thread before it was split.
I don't know what you're saying... I just did x + 10 + y + x + 5 + y + 5 + 10 = 65 + 15
2x + 2y + 30 = 80
2x + 2y = 50
x + y = 25
(x + 5)(-x + 25) + 10x
= -x^2 + 25x - 5x + 125 + 10x
= -x^2 + 30x + 125
(x + 15)^2 = x^2 + 15x + 15x +225
= x^2 + 30x + 225
Therefore:
-1(x - 15)^2 - 225 + 125
= -1 (x - 15)^2 - 100
I think that might be wrong. After playing with the calculator on AlgebraHelp.com I realised it might be -1(x-15)^2 + 225 + 125 which then simplifies to
-1(x-15)^2 + 350 (corrected mistakes in other posts)?
We're not trying to find the perimeter, I don't understand why we would find the diagonal when it doesn't cut at a diagonal. :? You have EF and FA (which I originally missed) also so it's not a diagonal...? That is just so you can make it y = -x + 25 and make it into an equation.
So is -1(x-15)^2 + 350 right? How do I find the max value? Is it x=15 because say if it was 16 the brackets i.e. -1(16-15)^2 would be negative and the answer would be smaller? So the greatest value is 350?
pka said:
Graph the function \(\displaystyle \frac{1}{{f(x)}}\).
Look at the graph and answer you own question.
Whoever moved this topic left the questions at the bottom in and ahhh it doesn't make any sense.... Thanks for the reply. I have put the thing about 1/(f)x back in the other thread pka, it didn't make sense here. Sorry but I don't understand. I have graphed 1/5 and 1/6 and 1/7 but I don't know what I'm looking for. I wasn't talking about the pen question for 1/f(x) but the 2nd question from the other thread.
http://www.freemathhelp.com/forum/viewtopic.php?t=25644
I'm just not sure what you meant when you said:
\(\displaystyle \Rightarrow \quad \frac{1}{{f(x)}} \le \frac{1}{5}.\)
I thought it was the other way around. I don't know what the arrow signifies. Please can you explain this step (or in the other thread?)?
Thanks for any help. Reply appreciated.
