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#1 2007-01-22 03:45:06

jxharmon
Member
Registered: 2007-01-08
Posts: 104

finding more y-intercepts

how would you graph or maybe I should say how do you find more points on the y-intercept if the info you have is slope -2; y-intercept (0,4) in order to graph?

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#2 2007-01-22 04:51:45

mathsyperson
Moderator
Registered: 2005-06-22
Posts: 4,900

Re: finding more y-intercepts

If the slope is -2 and the y-intercept is (0,4), then the equation of the line is y=-2x+4.

From there, to find more co-ordinates you just need to pick a value for x, and substitute that into the equation to find what y will be.

For x=3: y = -2*3+4 = -6+4 = -2. ∴ (3,-2)
For x=-1: y = -2*-1+4 = 2+4 = 6. ∴ (-1,6)

And so on.


Why did the vector cross the road?
It wanted to be normal.

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#3 2007-01-22 04:52:36

pi man
Member
Registered: 2006-07-06
Posts: 251

Re: finding more y-intercepts

To graph, first plot the point (0,4).   The slope is -2.   The slope is "rise over run" so the denominator is the change in x and the numerator is the change in y.   A slope of -2 is the same as -2 / 1.   If x changes by 1 (the denominator), y changes by -2 (the numerator).   

Let's find another point on this line by increasing X by 1.   That gives us 1 (0+1).   Everytime X increases by 1, y decrease by 2 (slope is -2).   So the y value would be 2 (4-2).   Plot the point (1,2) and draw a line through (0,4) and (1,2) and you're done.

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#4 2007-01-22 05:25:13

jxharmon
Member
Registered: 2007-01-08
Posts: 104

Re: finding more y-intercepts

thanks alot so if slope is 5 and y-intercept: (0,-2)  y=5x -(-2); so I graph (0,-2) then slope is rise over run slope of  5 =5/1 so if x changes by 1 then y would change by 5 so y value would be 5(5-2) plot the point of (1,3) am I on the right track or did I not get something.

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#5 2007-01-22 07:26:17

pi man
Member
Registered: 2006-07-06
Posts: 251

Re: finding more y-intercepts

You're on the right track.  And to prove to yourself that it's right, plug your new point of (1,3) into your equation.   Your equation should be  y = 5x - 2 rather than y= 5x - (-2).   Plug in 1 for x and 3 for y: 
3 = 5(1) - 2
3=3   
Success.

Last edited by pi man (2007-01-22 07:27:46)

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