x1y1 = x2y2
Contrast that with the more common proportionality you'll see, which is DIRECT proportionality:
x1/y1 = x2/y2
Basically, what all this means is:
- If two variables are inversely proportional, one will go up as the other goes down.
- If two variables are directly proportional, they both go up at the same time.
If x and y are inversely proportional, then so are x2 and y2. And if those two are inversely proportional, taking the inverse of ONE of them will create direct proportionality. So 1/x2 is directly proportional to y2. That's answer choice (E).