(a+b-c)(a-b+c)+(b-a+c)•(b-a-c) =(a+b-c)(a-b+c)-(b-a+c)•(a-b+c) =(a-b+c)[a+b-c-(b-a+c)] =(a-b+c)(2a-2c) =2(a-b+c)(a-c).