Bằng 1

quả trứng có trước:))

Đáp số đâu?

\(8^n:2^n=4\)

\(\Rightarrow4^n=4\)

\(\Rightarrow n=1\)

sai rùi e ơi:"))

\(A=\dfrac{-1}{20}+\dfrac{-1}{30}+\dfrac{-1}{42}+\dfrac{-1}{56}+\dfrac{-1}{72}+\dfrac{-1}{90}\)

\(A=-\left(\dfrac{1}{4.5}+\dfrac{1}{5.6}+\dfrac{1}{6.7}+\dfrac{1}{7.8}+\dfrac{1}{8.9}+\dfrac{1}{9.10}\right)\)

\(A=-\left(\dfrac{1}{4}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{6}+\dfrac{1}{6}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{8}+\dfrac{1}{8}-\dfrac{1}{9}+\dfrac{1}{9}-\dfrac{1}{10}\right)\)

\(A=-\left(\dfrac{1}{4}-\dfrac{1}{10}\right)\)

\(A=-\dfrac{3}{20}\)

\(x+x\times\dfrac{1}{3}+\dfrac{5}{18}=1\dfrac{1}{6}\)

\(\dfrac{4}{3}\times x+\dfrac{5}{18}=\dfrac{7}{6}\)

\(\dfrac{4}{3}\times x=\dfrac{7}{6}-\dfrac{5}{18}\)

\(\dfrac{4}{3}\times x=\dfrac{8}{9}\)

\(x=\dfrac{8}{9}:\dfrac{4}{3}\)

\(x=\dfrac{2}{3}\)

`a)`\(A=2x\left(x+1\right)-2\left(x-1\right)\left(x+4\right)-5\)

\(A=2x^2+2x-\left(2x-2\right)\left(x+4\right)-5\)

\(A=2x^2+2x-\left(2x^2+8x-2x-8\right)-5\)

\(A=-4x+3\)

`b)`\(B=\left(2x-1\right)\left(2x+1\right)-4x\left(5-x\right)+\left(3-x\right)\left(x+4\right)\)

\(B=4x^2-1-20x+4x^2+3x+12-x^2-4x\)

\(B=7x^2+21x+11\)