x3+y3+z3-3xyz 和 x3+y3+z3+3xyz分解因式11

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x3+y3+z3-3xyz 和 x3+y3+z3+3xyz分解因式11
x3+y3+z3-3xyz 和 x3+y3+z3+3xyz分解因式
11

x3+y3+z3-3xyz 和 x3+y3+z3+3xyz分解因式11
x^3+y^3+z^3-3xyz
==[( x+y)^3-3x^2y-3xy^2]+z^3-3xyz
=[(x+y)^3+z^3]-(3x^2y+3xy^2+3xyz)
=(x+y+z)[(x+y)^2-(x+y)z+z^2]-3xy(x+y+z)
=(x+y+z)(x^2+y^2+2xy-xz-yz+z^2)-3xy(x+y+z)
=(x+y+z)(x^2+y^2+z^2-xy-xz-yz)
用到二个公式:
a^3+b^3=(a+b)(a^2-ab+b^2)
(a+b)^3=a^3+b^3+3a^2b+3ab^2
x^3+y^3+z^3+3xyz
似乎不好分解?

x3+y3+z3-3xyz =( x+y)^3++z3-3xyz-3x^2y-3xy^2
=(x+y+z)(x^2+y^2+2xy-xz-yz+z^2)-3xy(x+y+z)
=(x+y+z)(x^2+y^2+z^2-xy-xz-yz)