Simple high school maths question

[kikelinus]

So, when you have something like - ( - 2x), the first "-" changes the whole expression inside the brackets, so it becomes 2x (potitive).

My question is: when I have + (-2x), does it also change?...My opinion is that it does not change, and I am quite sure of that, but I have an excercise that says the following (its a fraction):

- sen x
+ (-------------)
- cos x - 1

and in the following step in this excercise, it becomes the following:

sen x
------------
cos x + 1

Can someone pless explain to me how that is achieved?
Thanks.

[kikelinus]

Sorry...the first fraction come out wrong...it is supposed to be like this:

+(-sen x / - cos x - 1)

[SLH]

A +ve multiplied/divided by a -ve gives a -ve
A +ve multiplied/divided by a +ve gives a +ve
A -ve multiplied/divided by a -ve gives a -ve


So, if the signs (+ve/-ve) are the same, it's positive, if they are different then it's negative

Think of +(-2x) as +1 multiplyed by -2x

So it's a +ve multiplied by a -ve, so the answer will be -ve


Hope that helped

[siyan]

to go from that to the other thing multiply by (-1)/(-1)

-C

[Ambivalentiowa]

Inside your brackets, you have a negative divided by a negative. This produces a positive. Then when multiplied by a positive, it stays positive.

[mendhak]

-sinx = -(sinx)

-cosx-1 = - (cosx + 1)

divide and u get that. (yeah yeah I know I'm repeating but I think this explanation was ez)