去括号和加括号法则记忆口诀

去括号(正同负反乘进去)

a+(b+c) = a+b+c; a- (b+c) = a – b – c.

加括号(正同负反除出来)

a + b + c = a + ( b + c) ; a – b – c = a – ( b + c )

a – 2b –2 c = a –2 ( b + c )