<!-- BBCode Quote Start --><FONT COLOR=GREEN> IF a = b a^2 = ab a^2 - b^2 = ab - b^2 ( a + b ) ( a - b ) = b ( a - b ) ( a + b ) = b a + a = a 2 a = a 2 = 1 <-?? 註:"^2"是"平方"的意思 </FONT><!-- BBCode Quote End --> There is a flaw in the logic. Assume a = b, therefore a-b = 0 Going fr...