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Question 247277: Hi, I am having such trouble with these equations. My book goes over one example in which does not help me for this and others. Is there a simpler way of solving these equations? If not, a nice step-by-step would be great! I have a final next week and cannot get this to sink in. Here's an example equation.
15x-10y=-1
15y=-2+5x
I'm supposed to solve using substitution. When I add part of the equation to another, I get lost? I'm supposed to end up with an ordered pair.
Thank you so much!
Lise
Answer by richwmiller(17219)   (Show Source):
You can put this solution on YOUR website! 15x-10y=-1
15y=-2+5x
You should end up with one x and one y (x,y)
which will be the point the two lines cross(intersect).
solving by substitution means we solve one of the equations for x or y and then substitute that in the other equation.
15y=-2+5x
add 2 to both sides
15y+2=5x
divide by 5
(15y+2)/5=x
3y+2/5=x
put that in first equation
15(3y+2/5)-10y=-1
45y+30/5-10y=-1
45y-10y+6=-1
combine and subtract 6 from both sides
35y=-7
y=-7/35=-1/5=.2
15y=-2+5x
15(-1/5)=-2+5x
-3=-2+5x
add 2 to both sides
-1=5x
divide both sides by 5
-1/5=x=.2
so the point (ordered pair) is (-.2,-.2) or (-1/5,-1/5)
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