Prove

之前看到这题数学题， 好像很有趣， 放上来让大家看看:

Prove that:

a . 0 = 0, which a is a number.

Solution:

x + 0 = x for all x in real number
if x = 0,
0 + 0 = 0
a . (0 + 0) = a . 0
a . 0 + a . 0 = a . 0
a . 0 + a . 0 - a . 0 = 0
thus,
a . 0 =0