Why does?
Why does an equation for a line have to equal zero?![]()
7x = 21
7x - 21 = 0
7 =
x =
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.