Ta có (a+2)³-(a+6)(a²+12)+64=a³+6a²+12a+8-a³-12a-6a²-72+64=0(đpcm)

\(\left(a+2^3\right)-\left(a+6\right).\left(a^2+12\right)+64=0\)

\(\Leftrightarrow\left(a+8\right)-\left(a^3+6a^2+12a+72\right)=-64\)

\(\Leftrightarrow\left(a^3+6a^2+12a+72\right)-\left(a+8\right)=64\)

\(\Leftrightarrow a^3+6a^2+11a+64=64\)

\(\Leftrightarrow a^3+6a^2+11a^2=0\)

\(\Leftrightarrow a.\left(a^2+6a+11\right)=0\)

\(\Leftrightarrow a.\left[\left(a^2+2.a.3+9\right)+2\right]=0\)

\(\Leftrightarrow a.\left[\left(a+3\right)^2+2\right]=0\)

\(\Leftrightarrow\left[{}\begin{matrix}a=0\\\left(a+3\right)^2+2=0\left(\text{Vô lí}\right)\end{matrix}\right.\)

\(\Rightarrow a=0\)

\(\Rightarrow\) Đpcm.

Có sai đề không bạn

Biểu thức trên có nghiệm mà

1/ x^3+6x^2+12x+8=0

(x+2)^3=0

x+2=0

x=-2

Vậy x=-2

\(a^2\left(a+1\right)+2a\left(a+1\right)=a\left(a+1\right)\left(a+2\right)\) là 3 số nguyên liên tiếp nên chia hết cho 6

a: a^3-a=a(a^2-1)

=a(a-1)(a+1)

Vì a;a-1;a+1 là ba số liên tiếp

nên a(a-1)(a+1) chia hết cho 3!=6

=>a^3-a chia hết cho 6

\(a=\sqrt[3]{2-\sqrt{3}}+\sqrt[3]{2+\sqrt{3}}\)

=>\(a^3=2-\sqrt{3}+2+\sqrt{3}+3\cdot\left(\sqrt[3]{2-\sqrt{3}}+\sqrt[3]{2+\sqrt{3}}\right)\cdot\sqrt[3]{\left(2-\sqrt{3}\right)\left(2+\sqrt{3}\right)}\)

=>\(a^3=4+3a\)

=>\(a^3-3a=4\)

\(\Leftrightarrow a^2-3=\dfrac{4}{a}\)

\(\left(a^2-3\right)^3\)

\(=\left(\dfrac{4}{a}\right)^3=\dfrac{64}{a^3}\)

\(C=\dfrac{64}{\left(a^2-3\right)^3}-3a\)

\(=64:\dfrac{64}{a^3}-3a\)

=a^3-3a

=4