(12+23+34)×(23+35+45)—(12+23+34+45)×(23+35)=(12+23+34)×(23+35）+(12+23+34)×45—(12+23+34)×(23+35)-45×(23+35)=(12+23+34)×(23+35）—(12+23+34)×(23+35)+(12+23+34)×45-45×(23+35)=(12+23+34-23-35)×45=11×45=495
