Bán kính là \(20,096:3,14:2=3,2\left(m\right)\)

Diện tích là \(3,2\times3,2\times3,14=32,1536\left(m^2\right)\)

\(\Rightarrow\left[{}\begin{matrix}2x+1=3\\2x+1=-3\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}2x=2\\2x=-4\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=1\\x=-2\end{matrix}\right.\)

Cạnh AC dài \(10:\dfrac{1}{3}=30\left(cm\right)\)

Diện tích ABC là \(\dfrac{1}{2}\times30\times10=150\left(cm\right)\)

\(=125\times\left(56:7\right)=125\times8=1000\)

\(a,\text{Gọi }d=ƯCLN\left(n,n+1\right)\\ \Rightarrow n⋮d;n+1⋮d\\ \Rightarrow n+1-n⋮d\\ \Rightarrow1⋮d\Rightarrow d=1\RightarrowƯCLN\left(n,n+1\right)=1\\ \RightarrowĐpcm\\ b,\text{Gọi }d=ƯCLN\left(2n+1,2n\right)\\ \Rightarrow2n+1⋮d;2n⋮d\\ \Rightarrow2n+1-2n=1⋮d\\ \Rightarrow d=1\\ \RightarrowƯCLN\left(2n+1,2n\right)=1\\ \RightarrowĐpcm\\ c,\text{Gọi }d=ƯCLN\left(n+1,2n+3\right)\\ \Rightarrow n+1⋮d;2n+3⋮d\\ \Rightarrow2n+3-2\left(n+1\right)=1⋮d\\ \Rightarrow d=1\\ \RightarrowƯCLN\left(n+1,2n+3\right)=1\\ \RightarrowĐpcm\)

\(a,\Rightarrow2\left(x+5\right)-12=-20\\ \Rightarrow2\left(x+5\right)=-8\\ \Rightarrow x+5=-4\Rightarrow x=-9\\ b,\Rightarrow x-28+x=-24\\ \Rightarrow2x=4\Rightarrow x=2\\ c,\Rightarrow6\left(x-2\right)^3=-384\\ \Rightarrow\left(x-2\right)^3=-64=\left(-4\right)^3\\ \Rightarrow x-2=-4\Rightarrow x=-2\\ d,\Rightarrow2^x\left(1+2^3\right)=72\\ \Rightarrow2^x\cdot9=72\\ \Rightarrow2^x=8=2^3\Rightarrow x=3\)

\(\Rightarrow\dfrac{x}{3}=\dfrac{y}{2};\dfrac{y}{5}=\dfrac{z}{4}\\ \Rightarrow\dfrac{x}{15}=\dfrac{y}{10}=\dfrac{z}{8}=\dfrac{4x-3y+5z}{60-30+40}=\dfrac{7}{70}=\dfrac{1}{10}\\ \Rightarrow\left\{{}\begin{matrix}x=\dfrac{15}{10}=\dfrac{3}{2}\\y=1\\z=\dfrac{8}{10}=\dfrac{4}{5}\end{matrix}\right.\)