# Thread: Ax + By - C = 0

1. ## Ax + By - C = 0

Why does $\displaystyle Ax + By - C = 0$ ?

Why does an equation for a line have to equal zero?

2. Originally Posted by TheBerkeleyBoss
Why does $\displaystyle Ax + By - C = 0$ ?

Why does an equation for a line have to equal zero?
This is just another way of writing the equation of a line in "standard form."

Standard form is:

$\displaystyle Ax + By = C$

The only thing different with your equation is that you have subtracted C from both sides.

3. Originally Posted by TheBerkeleyBoss
Why does $\displaystyle Ax + By - C = 0$ ?

Why does an equation for a line have to equal zero?
7x = 21

7x - 21 = 0

7 = $\displaystyle \dfrac{21}{x}$

x = $\displaystyle \dfrac{21}{7}$

You can write the equation in may ways, but when you have the equation equated to zero, it is called "standard form"

Someone called it that, and others must have thought it more appropriate than "subtract all of the variables on the LHS (or RHS) from the other side and simplify" form.