(2a-b)(a+b-c)-(a+2ab)(a-b+c)+3c(a+b)
2a²+2ab-2ac-ab-b²+bc-(a²-ab+ac+2a²b-2ab²+2abc)+3ac+3bc
2a²+2ab-2ac-ab-b²+bc-a²+ab-ac-2a²b+2ab²-2abc+3ac+3bc
a²+2ab-b²+4bc-2a²b+2ab²-2abc
(2a-b)(a+b-c)-(a+2ab)(a-b+c)+3c(a+b)
2a²+2ab-2ac-ab-b²+bc-(a²-ab+ac+2a²b-2ab²+2abc)+3ac+3bc
2a²+2ab-2ac-ab-b²+bc-a²+ab-ac-2a²b+2ab²-2abc+3ac+3bc
a²+2ab-b²+4bc-2a²b+2ab²-2abc