Phân tích :
a.x ³-y ³+z ³+3xyz
b.a ³+b ³-c ³+3abc
c.x ³-y ³-z ³-3xyz
d.m ³+n ³-p ³
e.(x-y-z) ³-x ³+y ³+z ³
f.2x^4-21x ²+1
g.2x ²-3xy-6y ²
Phân tích : a.x ³-y ³+z ³+3xyz b.a ³+b ³-c ³+3abc c.x ³-y ³-z ³-3xyz d.m ³+n ³-p ³ e.(x-y-z) ³-x ³+y ³+z ³ f.2x^4-21x ²+1 g.2x ²-3xy-6y ²
By Savannah
Đáp án:
a, Ta có:
x ³-y ³+z ³+3xyz
= (x+y)³ – 3xy(x-y) + z³ – 3xyz
= [(x+y)³ + z³] – 3xy(x+y+z)
= (x+y+z)³ – 3z(x+y)(x+y+z) – 3xy(x-y-z)
= (x+y+z)[(x+y+z)² – 3z(x+y) – 3xy]
= (x+y+z)(x² + y² + z² + 2xy + 2xz + 2yz – 3xz – 3yz – 3xy)
= (x+y+z)(x² + y² + z² – xy – xz – yz)
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