If A ∝ B then :
B ∝ 1/A
B ∝ A
B = 1/A
B = A
If A ∝ B then we can say that A = kB (where k = non-zero constant)
⇒ B = (1/k) * A
1/k = m which is another variation constant
⇒ B = mA
⇒ B ∝ A