# convention in straight line equation?

• Nov 13th 2013, 08:09 AM
AaPa
convention in straight line equation?
in most straight lines equations found in books i see that the sign of the constant is always kept positive even if it means keeping the other two coeff. negative. why?
• Nov 13th 2013, 08:27 AM
Plato
Re: convention in straight line equation?
Quote:

Originally Posted by AaPa
in most straight lines equations found in books i see that the sign of the constant is always kept positive even if it means keeping the other two coeff. negative. why?

That may well have been your experience, it is truly not mine.
I have been teaching mathematics for almost fifty years and I have never seen that convention.

In fact, I think it would highly unusual to see
$\displaystyle -2x-3y=4\text{ or even }-6x-y+7=0$.
• Nov 13th 2013, 08:43 AM
HallsofIvy
Re: convention in straight line equation?
Quote:

Originally Posted by Plato
That may well have been your experience, it is truly not mine.
I have been teaching mathematics for almost fifty years and I have never seen that convention.

Since you were four!

Quote:

In fact, I think it would highly unusual to see
$\displaystyle -2x-3y=4\text{ or even }-6x-y+7=0$.
Far more common is to have the "leading" coefficient, typically the coefficient of x, positive.
• Nov 13th 2013, 09:10 AM
AaPa
Re: convention in straight line equation?
Quote:

Originally Posted by HallsofIvy
Far more common is to have the "leading" coefficient, typically the coefficient of x, positive.

Is there a reason for that?
• Nov 13th 2013, 10:01 AM
HallsofIvy
Re: convention in straight line equation?
It reduces the amount of typing because you don't have to type a "leading" +! I can type 4x- 3y= 7 with only 7 symbols. But -4x+ 3y= -7 has 9 symbols to type.