
Proportionality
Hello everyone!
This got me confused as I have not used proportionality for a very long time, all functions I deal with now are nonaffine.
If a is proportional to b and a is prortional to d, which of the following is correct:
(1)$\displaystyle a = k_1 b$ and $\displaystyle a = k_2 d$ so $\displaystyle a = \frac{k_1}{2}b + \frac{k_2}{2}d$
(2) $\displaystyle a = k_1 b + k_2 d $
(3) $\displaystyle a = k_3 bd$
Thank you!

First, observe that (1) actually contains an equivalent statement of the hypothesis:
$\displaystyle a = k_1b $ and $\displaystyle a = k_2c$
So any work should follow these.
Incidentally, if we add these and then divide by 2, we get (1).