12³:(3^-4.64) = 3³.4³:(3^-4.4³) = 3³.4³:(\(\frac{1}{3^4}\).4³)

=3³.4³:\(\frac{4^3}{3^4}\)= 3^3_.4³.3⁴ :4³= 3⁷

=2187

\(12^3:\left(3^{-4}.64\right)\)

\(=1728:\left(\frac{1}{81}.64\right)\)

\(=1728:\frac{64}{81}\)

\(=2187\)

4B = 1.2.3.4+2.3.4.4+....+(n-1).n.(n+1).4

= 1.2.3.4+2.3.4.(5-1)+....+(n-1).n.(n+1).[(n+2)-(n-2)]

= 1.2.3.4+2.3.4.5-1.2.3.4+....+(n-1).n.(n+1).(n+2)-(n-2).(n-1).n.(n+1)

= (n-1).n.(n+1).(n+2)

=> B = (n-1).n.(n+1).(n+2)/4

k mk nha

B = 1+ 1/x^2+y^2+2

Vì x^2 và y^2 đều >= 0 nên x^2+y^2>=0 => x^2+y^2+2 >= 2

=> 1/x^2+y^2+2 <= 1/2

=> B <=1+1/2 = 3/2

Dấu "=" xảy ra <=> x=0;y=0

Vậy GTLN của B = 3/2 <=> x=y=0

k mk nha

kết quả bằng 1 

\(\frac{1}{3}\)

dõ hơn nha bn

Có chân giả

bó tay :))))

\(\frac{2\frac{1}{2}x-1}{\frac{2}{3}}=\frac{\frac{-2}{3}}{1-2\frac{1}{2}x}\)         ĐKXĐ \(x\ne\frac{2}{5}\)

\(\Leftrightarrow\)\(\frac{\frac{5}{2}x-1}{\frac{2}{3}}=\frac{\frac{2}{3}}{\frac{5}{2}x-1}\)\(\Leftrightarrow\)\(\left(\frac{5}{2}x-1\right)^2=\frac{4}{9}\)\(\Leftrightarrow\)\(\frac{25}{4}x^2-5x+1=\frac{4}{9}\)

\(\Leftrightarrow\)\(\frac{25}{4}x^2-5x+\frac{5}{9}=0\)\(\Leftrightarrow\)\(\frac{25}{4}x^2-\frac{25}{6}x-\frac{5}{6}x+\frac{5}{9}=0\)

\(\Leftrightarrow\)\(\left(\frac{25}{4}x^2-\frac{25}{6}x\right)-\left(\frac{5}{6}x-\frac{5}{9}\right)=0\)\(\Leftrightarrow\)\(\frac{25}{2}x\left(\frac{1}{2}x-\frac{1}{3}\right)-\frac{5}{3}\left(\frac{1}{2}x-\frac{1}{3}\right)=0\)

\(\Leftrightarrow\)\(\left(\frac{25}{2}x-\frac{5}{3}\right)\left(\frac{1}{2}x-\frac{1}{3}\right)=0\)\(\Leftrightarrow\)\(\orbr{\begin{cases}x=\frac{2}{3}\\x=\frac{2}{15}\end{cases}}\)