Question

cos(-870)
Simplify......
I know to do such type of problems but this one has a - sign.... So does this minus go outside or should i keep it inside?
Sin(-x) is - sinx right? Should i use that?

Answer 1

Sure, use that.

Answer 2

Don't use that..... Cosines are rather.... Resistant to negatives.

Answer 3

Let me put it this way. When you're taking cosines (in radians or degrees) they're pretty much always positive within 90 degrees (or radians).

Answer 4

So it becomes - cos(870)
=-cos(720+150)
=-cos(150)
=-cos(180-30)
=(-)(-cos30)
=cos30?

Answer 5

The second you move out of that, though, it gets a little weird. We're know talking about a unit circle.

Answer 6

now*

Answer 7

So let's put it this way. If I have a circle, and I consider its center as an origin, everything on the left side of the circle is positive. Everything on the left side is negative. You with me?

Answer 8

There was a typo there.... Sorry.... Cos(-x) is cosx right?

Answer 9

Everything on the RIGHT side is positive. Everything on the LEFT is negative.

Answer 10

Precisely. You got it man.

Answer 11

So the answer is cos30?

Answer 12

Cos(-x) = Cos(x)
There's proofs and whatnot (what I was going to show you) but you got it.

Answer 13

Not quite.

Answer 14

Forgetting the unit circle.