# Thread: how to calculate this ... some algebra rule?

1. ## how to calculate this ... some algebra rule?

guys if I have something like this:

cos(theta)/x=r can I transpose this fomula as x=r*cos(theta) - is this correct?

btw. I am trying to understand if x-adjacent r-hypothenus x=r*cos(theta) -> I want to come up to this part while taking into consideration that cos(theta)=x/r

Taken at face value if $\displaystyle r = \dfrac{\cos \theta }{x} \text{ then } x = \dfrac{\cos \theta}{r}$

I suspect you want to show, using a right angled triangle that $\displaystyle x = r \cos \theta$.

If this is the case recall that by definition $\displaystyle \cos \theta = \dfrac{\text{adjacent}}{\text{hypotenuse}}$

3. could you please show me how to go step-by-step from: $\displaystyle \cos \theta = \dfrac{\text{x}}{\text{r}}$
to $\displaystyle x = r \cos \theta$ -> transpose formulae step is very important for me ... to understand what I look for

4. Multiply both sides by $\displaystyle r$

$\displaystyle r \cos \theta = \dfrac{x}{r} \cdot r = x$