Difference between plus minus and minus plus

**cosmonavt** · December 23rd 2011, 02:55 AM

In this page: LINK

In the second yellow table, they have an equation

Difference between plus minus and minus plus-capture.png

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?

**TheChaz** · December 23rd 2011, 03:00 AM

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!

**Plato** · December 23rd 2011, 03:04 AM

Originally Posted by cosmonavt

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

**cosmonavt** · December 23rd 2011, 04:14 AM

Thanks guys!

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