什麼是正比和反比

In fact, this is only mathematics and nothing to do with physics.

Two physical quantities are said to be proportional (正比) if doubling one of which leads to double the other.

E.g. presure and absolute temperature are in proportional in gas law. That means, if the absolute temperature is rasied to twice its initial value, the pressure will be doubled.

Two physical quantities are inversely proportional (反比) if double one of which leads to halve the other, and vice versa.

E.g. In gas law, pressure and volume are inversely proportional. That is, if the volume of a gas is halved, its pressure will be doubled.

以數字來算，正比是以正數增長，反比是負數增長。