**quick Help Please** (1 Viewer)

[heath]

i need to find the correlation between these two variables X and Y. given


_____X____Y__|
a_|__1__|__3__|
b_|__2__|__3__|
c_|__4__|__6__|
d_|__5__|__8__|

 

[nerdd]

i don't understand the question lol

 

[Rahul]

i think it may be to interpret as a table of values, like so.

x_|_1_|_2_|_4_|_5_|
y_|_3_|_3_|_6_|_8_|

and then try to come up with a relation, ie y = [something with x]

if that is so, its prett weird because two x values have the same y-value....seems a bit hard for 2u.

 

[Lazarus]

Correlation, as in, the correlation coefficient?

r ~ 0.94

But that's not in the 2u maths syllabus...

 

[heath]

yeah i thought cause it had two x values for the one y value that the correlation between the x and y values was a parabola

so i subed in 3 of the points (1,3) (2,3) (4,6) (5,8)

into the general equation y=ax^2 + bx +c

and got an equation by solving the three simultanously.

but the thing which stuffed me was; when i subed in the 4th point, it didn't satisfy.

that's why i posted here.

 

[Jeo]

omg, i wont say anything

 

[Lazarus]

Oh, you wanted to fit a curve to it?

A parabola doesn't seem to work... though a cubic does:

y = (-1/12)x³ + (13/12)x² - (8/3)x + (14/3)

 

[heath]

so how'd u work that out?

4 equations with 4 unknowns?

i don't think i can do that


and why did jesh say omg ???

tell me what ur thinking jesh.

 

[Lexicographer]

Originally posted by heath
and why did jesh say omg ???

tell me what ur thinking jesh.

You really want to know? He was just spamming.

 

[Huy]

Originally posted by Lexicographer
You really want to know? He was just spamming.

LOL, that's pretty much it...

 

[Rahul]

heath, are you certain that this isnt a mistake in the question. where is the question from?

 

[-=«MÄLÅÇhïtÊ»=-]

ye its a cubic curve

i fink all u gotta say is initially as x increases, y increases at a decreasing rate, then later y increases at an increasing rate.

 

[Lazarus]

What's wrong with solving four equations in four unknowns?

It just takes a while.

 

[heath]

ok man i did it, and got what u got. thanks

(p.s that did take a loong time) but good practice for my algebra skills

 

[Lexicographer]

How would you use those values to find the equation of the cubic? Is there a general formula, like ax+bx+cx+d=0?

 

[...]

thats what i thought...

i dunno..its something to do with the roots..turning pt (max and min)

 

[Lexicographer]

Laz? Help?

 

[Lazarus]

Originally posted by Lexicographer
How would you use those values to find the equation of the cubic? Is there a general formula, like ax+bx+cx+d=0?

Using y = ax+bx+cx+d, sub in each pair of x and y values to obtain four equations. Solve them all simultaneously to discover the values of the constants.

 

[Jeo]

 

[Lexicographer]

Thank you Laz!

Do you know if we have to be able to do that in 2 unit maths?

I've never come across it in any of our work, thought that could just be my negligence.