Posted by Cicilia on .
What is "3x=9" in y=mx+b form, and what is its slope, yintercept, and xintercept? [i think that its xintercept is (3,0), but i'm not sure about any of the others]
Also, what is the xintercept of "2y+16=0"? [is it "none"?]

Math: Linear Equations 
Willie,
I think these are trick questions and you have the right idea.
3x = 9 is the equation of a vertical line. There is no y in the equation, so there is no "y = mx + b" form for a vertical line. The simplest way to express this line is x = 3.
Its xintercept is 3 (because (3, 0) is where the line crosses the xaxis).
It does not have a yintercept, because the line never crosses the yaxis.
Technically, it has an undefined slope.
Similarly, the other equation is a horizontal line. 2y + 16 = 0 is the same as 2y = 16, or y = 8. This is a horizontal line through (0, 8). It has no xintercept. The yintercept is 8. The slope is zero. I think you are right to say that the xintercept is "none." 
Math: Linear Equations 
Cicilia,
Thanks!!! No wonder why these questions didn't make much sense and didn't seem quite possible to solve...

Math: Linear Equations 
Willie,
However, if the equation was this instead ...
2y + 16x = 0
... then you do have a diagonal line that has both an xintercept and a yintercept and a slope that is not zero but not undefined. I think it is a negative slope.
Can you figure out the xintercept of the line? the yintercept of the line? and the slope of the line? Hint: When y = 0, what is x? That gives you one intercept. When x = 0, what is y? That gives you another intercept. Draw the line and see if you can find the slope.