选出你所听句子中出现的单词( )
A:cold
B:cool
C:cloudy
____
计算:____ ÷(﹣12xy)=﹣6x+2y﹣1
12+1 = 1×(2−1)(2+1)(2−1) = 2 ﹣1;
13+2 = 1×(3−2)(3+2)(3−2) = 3 ﹣ 2 ;
15+2 = 1×(5−2)(5+2)(5−2) = 5 ﹣2.
试求: