[zonkey]

ummmm im not sure if there's a math help thread, i looked for it, but i couldnt find it.

I was wondering if anyone could help me with this little problem..

I need to verify the following:

i already verified the first part, now i'm trying to verify that the middle equation is equal to the last one.

any help would be appreciated. thanks

[ChunJin]

Simplify and expand =).

Meaning start with this: s/[1 / tan(a) - 1 / tan( B )]. Then do some algebra to it (multiply stuff mostly).

I'll give a pretty basic example, I suppose:

2/( 1 / x + 1 / y) -> multiply by 1 in a x/x manner -> 2x / (1 + x/y), now multiply by 1 in a y/y manner, 2xy / (y + x)

See what happened there?

[skadoosh!]

ewwwww trig is smellyyyy
XD

[intricaciesx]

oh oh could anybody help me with my problem?
i'm assuming the topic starter received his answer from AngeloDS.

my questions is :

Suppose cot(x) = -4 and sin(x) < 0 .

Find: sin (x + pi/3) =

I got sin(x) = -1/(sqrt17)

My friend told me to use the addition formula sinAcosB + cosAsinB , but I dont know if that's right. Any help? Thanks in advance.

[ChunJin]

The problem wasn't much of a trig problem, more of an algebra problem. You just needed to expand what cot() meant, and then use some pretty useful algebra rules to show that they are indeed equal.

However, the second problem I'm confused.

sin(x + pi/3) = ???, it needs to equal something . And yes that rule works. However, I will assume that it equals zero? If so, then it's just simple algebra.

You use sin( a + b ) = sin(a)cos( b ) + cos(a)sin( b ). You know two things: sin(x) < 0, so it can't be zero or anything larger than zero. And you know that cot(x) = -4. It'd be helpful to try to get it in such a form, and then expand and solve for (x). Once you solve for x, see if it satisfies sin(x) < 0. Then ask yourself, "Could there multiple values?" As there may be with all trig type problems.

On a side note:
sin(a - b ) = sin(a)cos( b ) - cos(a)sin( b )