83. Please use the following 4 numbers (each number must be used exactly once, and the order can be changed), as well as “ $+$ 、 $-$ 、 $\times 、 \div$ ” and parentheses, to make 24:
(1) $7 、 12 、 9 、 12$;
(2) $3 、 9 、 5 、 9$.
Answer: (1) Not unique, for example: $9 \times 12-7 \times 12=24$
(2) Not unique, for example: $(9-3) \times(9-5)=24$