Thread: please do it completely plzzz
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Old January 3rd, 2008, 04:31 AM
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wingless wingless is offline
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(a + b + c)^2 = (a + b + c)(a + b + c) = a.a + a.b + a.c + b.a + b.b + b.c + c.a + c.b + c.c = a^2 + b^2 + c^2 + 2ab + 2ac + 2bc

So, take a=2x, b=-2y, c=-2z,
4x^2 + 4y^2 + 4z^2 - 8xy - 8xz + 8yz

Or you could do this without using a formula,

(2x - 2y - 2z)^2 = (2x - 2y - 2z)(2x - 2y - 2z) =4x^2 - 4xy - 4xz -4xy + 4y^2 + 4yz - 4xz + 4yz + 4z^2 = 4x^2 + 4y^2 + 4z^2 - 8xy - 8xz + 8yz
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