Math: Linear Equations
posted by Cicilia .
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"?]

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." 
Thanks!!! No wonder why these questions didn't make much sense and didn't seem quite possible to solve...

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.