Toán Lớp 8: Phần tíchhằng đẳng thức sau a) (a+b+c) ³ b) (a+b-c) ³ Giúp mk vs mk đang cần gấp Thanks

Question

Toán Lớp 8:  Phần tíchhằng đẳng thức sau   a) (a+b+c) ³ b) (a+b-c) ³ Giúp mk vs mk đang cần gấp  Thanks

tonhu12 · Answer

$a) (a+b+c)&sup3;$   $=$ [$(a+b)+c$]&sup3;     $=(a+b)&sup3;+c&sup3;+3(a+b)c[(a+b)+c]$     $=a&sup3;+b&sup3;+3ab(a+b)+c&sup3;+3(a+b)c[a+b+c]$     $=a&sup3;+b&sup3;+c&sup3;+3ab(a+b)+3ca(a+b)+3bc(a+b)+3c&sup2;(a+b)$     $=a&sup3;+b&sup3;+c&sup3;+3(a+b)[ab+bc+ca+c&sup2;]$     $=a&sup3;+b&sup3;+c&sup3;+3(a+b)[b(a+c)+c(a+c)]$     $=a&sup3;+b&sup3;+c&sup3;+3(a+b)(c+a)(b+c)$     $=a&sup3;+b&sup3;+c&sup3;+3(a+b)(b+c)(c+a)$     $b)(a+b-c)&sup3;$    $=[a+(b-c)]$   $=a&sup3;+(b-c)&sup3;+3a&sup2;(b-c)+3(b-c)&sup2;$   $=a&sup3;+b&sup3;-c&sup3;-3b&sup2;c+3bc&sup2;+3a&sup2;b-3a&sup2;c+3ab&sup2;+3ac&sup2;-6abc$   $=a&sup3;+b&sup3;-c&sup3;+3(a&sup2;b-a&sup2;c-b&sup2;c+b&sup2;a+bc&sup2;+ac&sup2;)-6abc$