1.
设y = a2＋b2＋c2－ab－bc－ac
2y = 2a2＋2b2＋2c2－2ab－2bc－2ac
2y = (a-b)2 + (a-c)2 + (b-c)2
2y = (-1)2 + (-2)2 + (-1)2
2y =1 + 4 + 1
y = 3
2.
1/2的7次方