\(y\times5,5+y:0,5=30\\ y\times5,5+y\times2=30\\ y\times\left(5,5+2\right)=30\\ y\times7,5=30\\ y=4\)

\(x^2-4x+8\\ =\left(x^2-2.x.2+4\right)+4\\ =\left(x-2\right)^2+4\\ \left(x-2\right)^2\ge0\Rightarrow x^2-4x+8\ge4\\ \left(đpcm\right)\)

\(2021-\left(146+2021\right)+\left(-46+146\right)\\ =2021-146-2021-46+146\\ =-46\)

C

\(a,\left(x+3\right)\left(5-x\right)=0\\ \Rightarrow\left\{{}\begin{matrix}x+3=0\\5-x=0\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}x=-3\\x=5\end{matrix}\right.\)

\(c,x+17⋮x+3\\ x+3+14⋮x+3\\ 14⋮x+3\\ x+3\inƯ\left(14\right)=\left\{\pm14;\pm7\pm2;\pm1\right\}\)

Từ đó bạn tìm những giá trị của x nha!

\(B=2020.2021.2022\\ B=\left(2021-1\right).2021.\left(2021+1\right)\\ B=\left(2021^2-1\right).2021\\ B=2021^3-2021\\ \Rightarrow A>B\)