# Math Help - Co-functions help needed..

1. ## Co-functions help needed..

Hey guys,
Due to the lecturer not knowing himself, I don't know how exactly to approach some of the following problems.

Simplify:
1. sec(90°+x)sin(180°+x) + sin(-x)

2. __sin(-x)_ ______1______ __tanx___
sin(180°+x) + secx.sin(90°+x) - cot(90°+x)

Solve for x:
1. 3cot(90°+x) = tanx.sinx

2. tan(90°-x) = sec(3x+10°)cotx

I feel a bit stupid asking, BUT then, the only stupid question is the one not asked!

Riaan.

2. ## Re: Co-functions help needed..

Originally Posted by riaanj
Simplify:
1. sec(90°+x)sin(180°+x) + sin(-x)
The first thing I usually do is to get everything in terms of sine and cosine. sec(x) = 1/cos(x), and we have the sum of angles formula:
$cos(a + b) = cos(a) ~ cos(b) - sin(a) ~ sin(b)$

So what is $cos( 90 + x)$?

The same goes for sine:
$sin(a + b) = sin(a) ~ cos(b) + sin(b) ~ cos(a)$

See what you can do with this. If you need more help with it, simply ask.

-Dan

3. ## Re: Co-functions help needed..

Ok, so I had class tonight and I'm gonna try this one quick..
sec(90°+x)sin(180°+x) + sin(-x)
= -cscx(-sinx)+(-sinx)
= -1/sinx(-sinx)-sinx
= 1-sinx

I'll try the rest after I had some sleep..