(5x+4y-2z)(5x-4y-2z)
=[(5x-2z)+4y][(5x-2z)-4y]
=(5x-2z)^2-(4y)^2
=25x^2-20xz+4z^2-16y^2
(5x+4y-2z)(5x-4y-2z)=?
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