A:165°
B:120°
C:150°
D:135°
例1: 12+1 = 2−1(2+1)(2−1) = 2−1(2)2−1 = 2−11 = 2 ﹣1.
例2: 13+2 = 3 ﹣ 2 , 14+3 = 4 ﹣ 3 , 15+4 = 5 ﹣ 4
利用以上结论解答以下问题: