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Difference between plus minus and minus plus

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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?

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!

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:

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

Re: Difference between plus minus and minus plus