GCSE Maths Question

Etaqua · 7 Apr 2006 at 20:46

I'm stuck with finding equations from exponential graphs. I can do quadratics - no problem. But these just seem a lot harder.

There is an example of how to find quadratic equations from graphs in the CGP revision guide, but not exponentials. The "Acid Test" question asks you: "The graph shown here is thought to be represented by the equation Y = PQ^x where P and Q are unknown constants. Use the graph to find the values of P and Q".

Since you don't have a copy of the graph, I'll give you the two points I found on it: (0, 50) and (2, 100). In the method they say you need two points, preferably on either the X-axis or Y-axis, only one is.

Could someone give me a walkthrough of how to do it and questions like this?

TIA, Etaqua.

penski · 7 Apr 2006 at 20:47

Do your own homework, boyo.

*n

Etaqua · 7 Apr 2006 at 20:48

It's not homework, it's a page in the CGP revision guide.

Edit: I already have the answers, they're in the back of the book, but I don't know how to do this type of question.

Q = 1.41 and P = 50, if you need proof I'm not cheating on some homework.

penski · 7 Apr 2006 at 20:48

homework tbh.

*n

SaBBz · 7 Apr 2006 at 20:50

Take logs? Although ln (0) doesn't work....

Etaqua · 7 Apr 2006 at 20:52

Mmm, I don't think we do logs at GCSE stage, so I don't think that's how we're supposed to do it. There is no mention of them on the page which (doesn't) explains how to solve them.

Yewen · 7 Apr 2006 at 21:11

If you want to add me to msn, I can see if my brain remembers back 12 months, I may be able to help.

sag-okia at zen.co uk

Amleto · 7 Apr 2006 at 21:15

It's quite easy - just stick in x=0, and you find P trivially, then stick in the other point!

explicity:

consider y=PQ^x @ (0,50)

=>50 = P

.:
100 = 50Q^2 (considering (x,y) = (2,100))
=>2 = Q^2

.: Q = +/- sqrt(2)

Etaqua · 7 Apr 2006 at 21:31

Amleto, you are a lifesaver. You also reminded me that x^0 is not 0, but 1. I think that's where I went wrong...

Thanks @ Amleto.

*hands Amleto a beer and young woman*

Amleto · 7 Apr 2006 at 21:47

Etaqua said:
Amleto, you are a lifesaver. You also reminded me that x^0 is not 0, but 1. I think that's where I went wrong...

Thanks @ Amleto.

*hands Amleto a beer and young woman*

Killerkebab · 7 Apr 2006 at 22:21

Etaqua said:
*hands Amleto a beer and young woman*

Does she look like a man?

Amleto · 7 Apr 2006 at 22:40

Killerkebab said:
Does she look like a man?

:\

iSam · 7 Apr 2006 at 22:48

Etaqua said:
*hands Amleto a beer and young woman*

PIMP!

VeNT · 7 Apr 2006 at 22:49

iirc, theres RULES about posting homework questions on these here forums, so you godda ask your self..........do I feel lucky?

well? do you punk?

iSam · 7 Apr 2006 at 22:56

VeNT said:
iirc, theres RULES about posting homework questions on these here forums, so you godda ask your self..........do I feel lucky?

well? do you punk?

spirit · 7 Apr 2006 at 23:09

i love those films. sadly i only have two of them on dvd!

iSam · 7 Apr 2006 at 23:56

Aye, they are classics alright!

VeNT · 8 Apr 2006 at 11:36

Isotope said:

tbh I was quoting from dirty harry (i think)

spirit · 8 Apr 2006 at 11:42

VeNT said:
tbh I was quoting from dirty harry (i think)

yes, it was. but those films still rock and he is way cooler in them

iSam · 8 Apr 2006 at 13:45

VeNT said:
tbh I was quoting from dirty harry (i think)

Ah well, I just found what I could!