1/j = 1/u + 1/v

to make u the subject. I know the answer is u = jv / v-j and I can get as far as:

1/j = v+u / uv

but I just can't see how to get any further. Please can anyone help??

Thanks, Andrew

1/j = 1/u + 1/v (start)

So let's get rid of the denominators, because fractions suck.

1 = j/u + j/v (*j)
u = j + ju/v (*u)
uv = jv + ju (*v)

The denominators done, u's to one side...

uv - ju = jv (-ju)

And it might be trickier to notice, but since it's all like terms...

uv - uj = jv (same)
u(v-j) = jv (factor)

Yeah, see what I did there? Yep. Div it out, and quit banging your forehead on the keyboard, I didn't notice it for a sec either.