giai giup cho to nghe

L

linhhuyenvuong

Tu a+b+c+d=0 \Rightarrowb+c=-(a+d )\Rightarrow(a+b)^3=-(a+d)^3.Ma (b+c)^3=b^3+c^3+3bc(b+c) va -(a+d)^3=-a^3-d^3-3ad(a+d).\Rightarrowb^3+c^3+3bc(b+c)=-a^3-d^3-3ad(a+d)
\Rightarrowa^3+b^3+c^3+d^3=-3ad(a+d)-3bc(b+c)(**1)
thay -(a+d)=b+c vao -3ad(a+d) -3bc(b+c) ta duoc 3ad(b+c)-3bc(b+c)=3(b+c)(ad-bc)(**2). Tu(**1)(**2) \Rightarrowa^3+b^3+c^3+d^3=3(b+c)(ad-bc)
Nho nhan nut cam on nha
 
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V

vi_tieu_bao_2010

linhhuyenvuong said:
Tu a+b+c+d=0 \Rightarrowb+c=-(a+d )\Rightarrow(a+b)^3=-(a+d)^3.Ma (b+c)^3=b^3+c^3+3bc(b+c) va -(a+d)^3=-a^3-d^3-3ad(a+d).\Rightarrowb^3+c^3+3bc(b+c)=-a^3-d^3-3ad(a+d)
\Rightarrowa^3+b^3+c^3+d^3=-3ad(a+d)-3bc(b+c)(**1)
thay -(a+d)=b+c vao -3ad(a+d) -3bc(b+c) ta duoc 3ad(b+c)-3bc(b+c)=3(b+c)(ad-bc)(**2). Tu(**1)(**2) \Rightarrowa^3+b^3+c^3+d^3=3(b+c)(ad-bc)
Nho nhan nut cam on nha
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