Em cần dán giấy màu kín bên ngoài cho cái hộp đựng bút dạng hình lập phương không có nắp có cạnh dài  6cm. Vậy diện tích giấy màu cần dán là ....................

\(x^4+x^3+x+1=0\)

\(\Rightarrow\left(x^4+x^3\right)+\left(x+1\right)=0\)

\(\Rightarrow x^3\left(x+1\right)+1\left(x+1\right)=0\)

\(\Rightarrow\left(x^3+1\right)\left(x+1\right)=0\)

\(\Rightarrow x=-1\)

Gía trị của biểu thức 8 x 5 + 4

A. 40                     

B. 41                          

C.   44

\(\left(x^2+3x+2\right)\left(x^2+7x+12\right)=24\)

\(\Rightarrow\left(x+1\right)\left(x+2\right)\left(x+3\right)\left(x+4\right)=24\)

\(\Rightarrow\left(x+1\right)\left(x+4\right)\left(x+2\right)\left(x+3\right)=24\)

\(\Rightarrow\left(x^2+4x+x+4\right)\left(x^2+3x+2x+6\right)=24\)

\(\Rightarrow\left(x^2+5x+4\right)\left(x^2+5x+6\right)=24\)

\(\Rightarrow\left(x^2+5x+5-1\right)\left(x^2+5x+5+1\right)=24\)

\(\Rightarrow\left(x^2+5x+5\right)^2-1=24\)

\(\Rightarrow\left(x^2+5x+5\right)^2=25\)

\(\Rightarrow\left(x^2+5x+5\right)^2-25=0\)

\(\Rightarrow\left(x^2+5x+5+5\right)\left(x^2+5x+5-5\right)=0\)

\(\Rightarrow\left(x^2+5x+10\right)\left(x^2+5x\right)=0\)

\(\Rightarrow\left(x^2+5x+\dfrac{25}{4}+\dfrac{15}{4}\right)\left(x^2+5x\right)=0\)

\(\Rightarrow\left[\left(x^2+5x+\dfrac{25}{4}\right)+\dfrac{15}{4}\right]\left(x^2+5x\right)=0\)

\(\Rightarrow x\left(x+5\right)\left[\left(x+\dfrac{5}{2}\right)^2+\dfrac{15}{4}\right]=0\)

\(\Rightarrow\left[{}\begin{matrix}x=0\\x=-5\\\left(x+\dfrac{5}{2}\right)^2+\dfrac{15}{4}>0\end{matrix}\right.\)

\(a_1+a_2+a_3+a_4+...+a_{19}+a_{20}+a_{21}=10\)

\(\Rightarrow\left(a_1+a_2\right)+\left(a_3+a_4\right)+...+\left(a_{19}+a_{20}\right)+a_{21}=10\)

\(\Rightarrow1+1+...+1+a_{21}=10\)

\(\Rightarrow10+a_{21}=10\)

\(\Rightarrow a_{21}=0\)

Mà \(a_{20}+a_{21}=2\Leftrightarrow a_{20}=2\)