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Question 79300: find the coordinates of the x and y intercepts of 3x +9y = -54
Answer by mathdoc314(58)   (Show Source):
You can put this solution on YOUR website! Oh I love this one
An image leaps into my mind of a diagram on a blackboard with an x axis, and a y axis, and a tilted line that comes in from the upper left, crosses the x axis on its way down, and crosses the y axis somewhere below the origin before it exits the diagram. Of course lines are bidirectional but I imagine this one coming in from the left.
Anyway to get the intercepts you plug in 0 for one of the variables.
Like if you plug in 0 for x then your equation is: 9y = -54
You solve that and get y = -6
This gives you a point on the line (0,-6) (x=0, y=-6)
Since x is zero that means you have not gone to the left or the right on the x axis, so you have not moved horizontally at all from the center of the diagram. All you do is move 6 units down from the center of the origin to find this point, on the y axis. That is the y-intercept, when x is zero.
Also you put in y=0 and find x
3x = -54
x = -18
Your point on the line is (-18,0)
This is a point way 18 spaces directly left of the origin. It is the x-intercept, the point where the line intercepts the x-axis. Remember you got it by putting in y=0, because x is the variable here that has a value.
I encourage you to draw the diagram and find some other points on the line and be amazed by how nicely the numbers fit the equation (if your line is straight and you used graph paper. Graph paper is great for these.)
Good luck in your math
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