1. ## 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 non-affine.

If a is proportional to b and a is prortional to d, which of the following is correct:

(1) $a = k_1 b$ and $a = k_2 d$ so $a = \frac{k_1}{2}b + \frac{k_2}{2}d$
(2) $a = k_1 b + k_2 d$
(3) $a = k_3 bd$

Thank you!

2. First, observe that (1) actually contains an equivalent statement of the hypothesis:
$a = k_1b$ and $a = k_2c$

So any work should follow these.
Incidentally, if we add these and then divide by 2, we get (1).