# Thread: Graphs using slope and y intercept

1. ## Graphs using slope and y intercept

I'm just going to link a picture to the question in my book since I have no idea how I would even attempt to draw a graph on here manually.

Basically, I don't understand why in the equation "y = -2/3x - 3" when they go to plot it on the graph, they're making the -3 a positive 3 instead, and there are other parts in the book that have a similar equation where both the slope and the y intercept are negatives, but they use both as positives when turning it into the graph portion, and I really don't understand why.

Any help would be much appreciated in understanding why that is.

mathproblem_zpsa6456c35.png Photo by Azuraiiii | Photobucket

2. ## Re: Graphs using slope and y intercept

I plotted $\displaystyle y = -\displaystyle\frac{2}{3}x - 3$ $\displaystyle \slope$ on my 3D grapher and the line I got intercepted the y-axis at $\displaystyle \slope$ $\displaystyle -3$ $\displaystyle \slope$ not $\displaystyle +3$. The line they plotted in Photobucket is the equation $\displaystyle \space$ $\displaystyle y = -\displaystyle\frac{2}{3}x + 3$. I would say that it is incorrect. Your y-intercept is clearly $\displaystyle \slope$ $\displaystyle -3$.

3. ## Re: Graphs using slope and y intercept

there should be no confusion as far as slope intercept form is concerned. for the equation y = -2/3 x - 3, the y intercept is -3 and the coordinates of the point will be ( 0, -3 ). The slope is - 2/3 this one mas consider 9 -2 ) / 3 OR 2 / ( -3 ) and locate the next point and then draw the line. Anything otherwise would be wrong.

4. ## Re: Graphs using slope and y intercept

Thanks for the confirmations, I thought I was losing it for a second there.

5. ## Re: Graphs using slope and y intercept

Strange, but Wolfram Alpha agrees with your book. http://www.wolframalpha.com/input/?t=crmtb01&f=ob&i=plot%20-(2%2F3)%20x%20-3

6. ## Re: Graphs using slope and y intercept

Nooo, why did you have to say that, now I'm back to questioning myself again!

7. ## Re: Graphs using slope and y intercept

Originally Posted by ReneG

the second graph is correct. If you notice on the first graph, the y-axis is not at the origin.