\(A=\frac{12n+1}{30n+2}=2\Leftrightarrow12n+1=60n+4\Leftrightarrow60n+4-12n-1=0\Leftrightarrow48n+3=0\Leftrightarrow16n+1=0\Leftrightarrow n=\frac{-1}{16}\)

\(=\frac{101}{101}\times\frac{100}{99}\times\frac{99}{98}\times\frac{98}{97}\times......\times\frac{2}{1}=\frac{101\times100\times99\times....\times2}{101\times99\times98\times97\times.....1}=100\)

a)1/2:0,5-1/4:0,25+1/8:0,125-1/10:0,1

=1/2x2-1/4x4+1/8x8-1/10x10

=1-1+1-1

=0

b)không biết k 2 cái là dc rồi

\(x^2-5x+4=0\Leftrightarrow x^2-4x-x+4=0\Leftrightarrow x\left(x-4\right)-\left(x-4\right)=0\Leftrightarrow\left(x-1\right)\left(x-4\right)=0\Leftrightarrow\left[{}\begin{matrix}x-1=0\\x-4=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=1\\x=4\end{matrix}\right..Vậy:x\in\left\{1;4\right\}\)

tớ nghĩ đề là thế này