# Homework Help: Proof of y-intercept

1. Jun 8, 2010

### dance_sg

1. The problem statement, all variables and given/known data

Prove or Disprove: In the equation y=mx+b, b is the y-intercept.

3. The attempt at a solution

I know that this statement is true, and i know that to prove anything im suppossed to use a formula, not give examples. but how should i go about doing this if the formula is the question?

2. Jun 8, 2010

### rock.freak667

At any point on the y-axis, what is the x-coordinate?

3. Jun 11, 2010

### Shaybay92

The y intercept occurs when x = 0 right.... that is the definition of the y intercept. Thus:

y = 0x + b... y = b
There is no real other way to prove this that isnt just being really obvious...

4. Jun 11, 2010

### Mentallic

It seems to prove it to me. Even though it's obviously simple, it still does the job it's meant to.

For another "slightly" more complicated one, prove the y-intercept for the line ax+by+c=0 is always -c/b, where $b\neq 0$. This is basically the same thing, just a bit more complicated since it wouldn't usually be done in 1 simple step. Getting to quadratics complicates things more-so.

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