HELP

[chemkid_23]

On qs 7 of exam 1 2008 for graphs and relations, how do you work it out?
It's this type of qs that I keep losing marks, and the assessor's report doesnt tell you how to do it.
Please help me out because I'm certain this type of qs will pop up come friday

[water_boy]

I always had trouble with this kind of question until I sought help from my teacher and I am pretty confident with them now.

You have a graph showing the relationship between Y and X^2, with the point (4,1) shown on the graph.
Firstly you let Y=1 and then you let X^2=4.

You sub those results into the formula Y=kX^2 and solve for k.

1=k4
k=1/4.

Therefore, Y=1/4X^2. Which is option C, the correct option.

[abzzzz]

How would you know to use that formula? this shit pisses me off!

how do you work this out?
An equation for the straight line that passes through the points (10, 1) and (4, –2) is
A. x + 2y = 12
B. 2x + y = 6
C. 4x + y = 14
D. x – 4y = 14
E. x – 2y = 8

And

The line above passes through the origin and the point (2, 1).  (the slope on the graph is negative)
The slope of this line is
A. –-2
B. –-1
C. − 1/2

D. 1/2


E. 2

[chemkid_23]

I always had trouble with this kind of question until I sought help from my teacher and I am pretty confident with them now.

You have a graph showing the relationship between Y and X^2, with the point (4,1) shown on the graph.
Firstly you let Y=1 and then you let X^2=4.

You sub those results into the formula Y=kX^2 and solve for k.

1=k4
k=1/4.

Therefore, Y=1/4X^2. Which is option C, the correct option.

that's what confuses me. Your working out is obviously correct, but when u sub in the coordinate, why doesnt the 4 get squared?
If y=kx^2, and u sub in (4,1), wouldnt it look like this  1=k x 4^2, so it would be 1=k x 16


That's what I did.

So basically when u sub in the point, dont square it???

[abzzzz]

I'd assume it's already squared

[chemkid_23]

So basically the equation is y=k2^2 which give u the coordinate (4,1)   ??
So then u just use that point to work out k
aha i think i get it now

[water_boy]

Yeah you have it right in your last post. If you get a different question with X^3 on the horizontal axis instead of X then you just sub the coordinates into Y=kX^3 and so on.
Sorry if this confuses you it is hard to explain online

[chemkid_23]

so everytime they giv us a graph of y=kx^2 or ^3, and they ask find the relationship or the graph that shows it between x and y, we just sub in the coordinate as it is, with the x coordinate taking the spot of the x^2 or x^3 respectively......