Straight line in a parabola

[Muzk]

How am I supposed to know where the line cuts the parabola?
And since I got this from google, why does it say
p:y=x²+2x-3 ? <- I don't get the 2x-3, obviously it has something to do with the position but I'm too stupid to see it, and wikipedia only helps Ph.D.
(btw I put the line in on my own)

Just tell me the way or some formula.. and explain, PLEASE ;_;

http://i362.photobucket.com/albums/oo69/MUZKROX/Parabel_scheitel_nullstellen.gif?t=1257699242

Help me >_>


A place for beginners and learners to ask their mathematical questions about theory or specific issues. Don't worry if you think your questions are stupid or pointless, ask away. Learning is not stupid and is never pointless.

[red cat]

You have not mentioned the equation of the line. So let it be: y= mx + c

The points where the parabola and the line intersect, will satisfy both of the equations.

So equate the values of y.

y= mx + c = x^2 + 2x -3

Then solve the quadratic: x^2 + (2-m)x +(-c-3) = 0

Then substitute the values of x in any of the equations to get the corresponding values for y.

[red cat]

Sorry, I overlooked some very simple things. The line passes through (1, 0) and (-4, -2). So its slope = m = ( 0 - (-2))/(1 - (-4)) = 0.4

Substituting x and y with their values at N2 we get

0 = m*1 + c
=> 0 = 0.4 + c
=> c= -0.4
So the quadratic equation becomes:

x^2 + (2-0.4)x +(0.4-3) = 0

=> x^2 + 1.6 * x -2.6 = 0

=>x = (-1.6 + (2.56 + 10.4)^0.5 )/2 , (-1.6 - (2.56 + 10.4)^0.5 )/2

=>x = (-1.6 + (12.96)^0.5 )/2 , (-1.6 - (12.96)^0.5 )/2

=>x = (-1.6 + 3.6)/2 , (-1.6 - 3.6)/2

=>x = 2/2 , -5.2/2

=>x = 1 , -2.6

Substituting the values of x in the equation of the parabola, we get:

y= 1^2 + 2*1 - 3 , (-2.6)^2 + 2*(-2.6) - 3
= 0 , 6.76 - 5.2 - 3
= 0 , 0.56 - 2
= 0 , -1.44

So the other point is (-2.6 , -1.44)

[GPDP]

And now for a crash course on Marxist mathematics:


How am I supposed to know where the line cuts the parabola?

Going by Marx's theorems, wherever the bourgeois parabola accumulates enough capital, there is greater likelihood of the proletarian line seizing the parabola's means of production, thus undercutting it.


And since I got this from google, why does it say
p:y=x²+2x-3 ? <- I don't get the 2x-3, obviously it has something to do with the position but I'm too stupid to see it, and wikipedia only helps Ph.D.
(btw I put the line in on my own)

Googlian mathematics are bourgeois nonsense, simple as that.

The proletarian line (in this case, 2x-3), being in a dialectical position to cut down the bourgeois parabola's domination of the grid, must be fooled into thinking it cannot do so, hence Google's deception.


Just tell me the way or some formula.. and explain, PLEASE ;_;

Help me >_>

The way forward for the proletarian line lies in the vanguard equation, which will point the way toward liberation from the differential equation of the bourgeois parabola.

[red cat]

How am I supposed to know where the line cuts the parabola?
And since I got this from google, why does it say
p:y=x²+2x-3 ? <- I don't get the 2x-3, obviously it has something to do with the position but I'm too stupid to see it, and wikipedia only helps Ph.D.
(btw I put the line in on my own)

Just tell me the way or some formula.. and explain, PLEASE ;_;

http://i362.photobucket.com/albums/oo69/MUZKROX/Parabel_scheitel_nullstellen.gif?t=1257699242

Help me >_>


A place for beginners and learners to ask their mathematical questions about theory or specific issues. Don't worry if you think your questions are stupid or pointless, ask away. Learning is not stupid and is never pointless.

So you put the line in yourself?

I have assumed that you wanted the line to pass through (-4, -2).

About the parabola, I think you have seen only the ones of the form y^2 = Ax.
Those pass through the origin. Here, notice that the origin has moved a horizontal distance of 1 and vertical distance of 4 units from where it should have been to get an equation of the above form. To make up for this translation of the coordinate system, its equation should be: y + 4 = (x + 1)^2 => y = x^2 + 2x - 3