# Difference between plus minus and minus plus

• Dec 23rd 2011, 02:55 AM
cosmonavt
Difference between plus minus and minus plus

In the second yellow table, they have an equation

Attachment 23132

Why exactly do they have different symbols, plus minus and minus plus?

Does it mean that if the first sign is minus then the other has to be plus and vice versa?
• Dec 23rd 2011, 03:00 AM
TheChaz
Re: Difference between plus minus and minus plus
The sign inside the parenthesis is the OPPOSITE of the sign between terms.
cos(x + y) = cos(x)cos(y) - sin(x)sin(y)

So yes, it means what you said!
• Dec 23rd 2011, 03:04 AM
Plato
Re: Difference between plus minus and minus plus
Quote:

Originally Posted by cosmonavt
Attachment 23132
Why exactly do they have different symbols, plus minus and minus plus?

It is shorthand notation.
When the first is plus the second is minus:
$\displaystyle \cos(x+y)=\cos(x)\cos(y)-\sin(x)\sin(y).$

When the first is minus the second is plus:
$\displaystyle \cos(x-y)=\cos(x)\cos(y)+\sin(x)\sin(y).$
• Dec 23rd 2011, 04:14 AM
cosmonavt
Re: Difference between plus minus and minus plus
Thanks guys!