Graphing Linear EquationsDate: 12/26/2001 at 23:26:31 From: Cindi Smith Subject: Slope-intercept: Graphing linear eqations Give the intercepts of 7x - 2y = 2. I recall doing something like this before but I do not want to steer my son wrong. Please help with this problem - maybe it will jar my memory and I will be able to help him with his studies. Thank you for your help. Date: 12/28/2001 at 18:45:47 From: Doctor Tim Subject: Re: Slope-intercept: Graphing linear eqations Thanks for writing, Cindi. The intercepts are where the graph crosses the x and y axes. And that happens where x = 0 (for the y axis) and y = 0 (for the x axis). If this seems backward, think about it until it comes clear. For an equation in the form you have, you find the x intercept by setting y = 0: 7x - 2(0) = 2 7x = 2 x = 2/7 And similarly for the y-intercept. Don't forget that you can always check by plugging in. If you put (x = 2/7, y = 0) into the equation, does it balance? Yes. That means that that point - (2/7,0) - is on the line. Note: "slope-intercept" form is where you solve for y first. In this case, to get y alone on one side, 7x - 2y = 2 add 7x to both sides -2y = 2 - 7x divide both sides by (-2) y = (7/2)x - 1 There, (7/2) is the slope, and -1 is the intercept (it's the y-intercept in this form). Most books write this y = mx+b Some write y = ax + b and some (especially statistics books) write y = a + bx but they all mean the same. - Doctor Tim, The Math Forum http://mathforum.org/dr.math/ |
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