第1个回答 2012-05-26
1.x^4 - xy^3 - x^3y - 3x^2y + 3xy^2+y^4=x^4+2x^2y^2+y^4-2x^2y^2- xy^3 - x^3y - 3x^2y + 3xy^2
=(x^2 -y^2)^2 -xy(x-y)^2 -3xy(x-y)
=(x+y)^2 -xy -3xy
=(x+y)^2 - 4xy =(x-y)^2 =1
2. a^2 + 2ab + b^2 - 2ac - 2bc + c^2=(a+b)^2 +(a-c)^2 + (b-c)^2 -a^2- b^2 -C^2
=(a+b+c)(a+b-c) + (a-b-c)(a+b-c) + (b-c-a)(a+b-c)
=(a+b-c)(a+b-c)=(a+b-c)^2
a=1/(3m)+1 ? , b=2/(3m)+2 ?
a =m/3 +1 ? b=2m/3 + 2 ?