# Trigonometric Equation

1. Aug 31, 2008

### Sabellic

1. The problem statement, all variables and given/known data
If cos x = a/b and tan x = c/d; where a, b, c do not equal 0, then sin x is.....

(a) bd/ac

2. Relevant equations

3. The attempt at a solution

The way I see it, if cos x = a/b, then b=hypotenuse.
if tan x = c/d, then d= hypotenuse (two hypotenuse values?) and c = opposite.

Therefore sin x = c/d. I don't know why the answers in the book use products of the vairables in their numerators and denominators.

2. Aug 31, 2008

### happyg1

Hmmm... Your c) and d) choices are the same..and the tan doesn't involve the hypotenuse.
Are you sure you copied the whole thing right?

Last edited: Aug 31, 2008
3. Sep 1, 2008

### HallsofIvy

Staff Emeritus
Since
$$tan \alpha= \frac{sin \alpha}{cos \alpha}$$
multiplying on both sides by $cos(\alpha)$ gives

$$sin(\alpha)= cos(\alpha)tan(\alpha)$$
That's all you need.