1. The idea that modern art can only be seen in museums is mistaken.
    那种认为现代艺术只能在博物馆里才能看到的观点是错误的。

2. You´re mistaken.
    你（搞）错了。

3. "My brother," he said, "you are quite mistaken.
    说道：“老兄，你大错特错了，