我擅长跳舞，但不会弹钢琴，李若妍擅长弹钢琴但不会跳舞

1) I'm good at dancing but not at playing piano, while Li Ruiyan is good at playing piano but not at dancing.

2) I'm good at dancing but not at playing piano. while Li Ruiyan does well the other way around.

反之亦然：恰恰相反。

i am good at dancing,but i can't play the Li Ruoyan is good at playing the panio and can't dance

I am good at dancing,poor in playing the piano,while li ruoyan does well in playing the piano,not good at dancing