Low correlation between variables of a formula and his result

Question

I have a pandas DataFrame with 40 variables, but someone of them are just ratios between other columns.

I got a correlation table with higher pairs (>|0,6|) but the surprise is:

The variable A= B/C

A correlation with B = 0,04

A correlation with C = -0,1

I understand than by separate they can not have correlation, [B with C] correlation with A=1

but is not spected that .corr() find that relation himself?

What do you think?