Verified answer

Mais j'aime les math plus que le reste parce que c'est là où je suis le plus fort.

Thorandthor : Your sentence is good but it change the meaning a little.

-What is asked : I like math because I'm good at it.

cause : I'm good at math.

consequence : I like it.

-Your sentence : I'm good at math because I like it.

cause : I like math.

consquence : I'm good at it.

I would say : Mais comme j'aime particulièrement les maths, il se trouve que c'est le sujet où je suis la plus forte (ou "le plus fort" if a guy is speaking).