# Thread: Difference between plus minus and minus plus

1. ## Difference between plus minus and minus plus

In the second yellow table, they have an equation

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?

2. ## 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!

3. ## Re: Difference between plus minus and minus plus

Originally Posted by cosmonavt

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:
$\cos(x+y)=\cos(x)\cos(y)-\sin(x)\sin(y).$

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

Thanks guys!