a = b
a + a = a + b
2a = a + b
2a - 2b = a + b - 2b
2(a - b) = a + b - 2b
2(a - b) = a - b
2X0 = 1X0
0=0
猴猴,,,厉害吧,2=1!(ZT)
a = b
a + a = a + b
2a = a + b
2a - 2b = a + b - 2b
2(a - b) = a + b - 2b
2(a - b) = a - b
2 = 1