当x=2-5,y=25时,
(x+y)(x-y)=x2-y2
=(2-5)2-(25)2
=(4-25+5)-20
=-11-25.
过去念书时,我接受知识很慢。
A.是
B.否
一______was your day off? 一Great!
A.Where
B.How
C.What
D.Why