\(\Leftrightarrow\frac{\left[\left(x-1\right):2+1\right]\left(x+1\right)}{2}=441\)
\(\Leftrightarrow\left(x+1\right)\left(\frac{x-1}{2}+1\right)=882\)
\(\Leftrightarrow\left(x+1\right)\left(\frac{x+1}{2}\right)=882\)
\(\Leftrightarrow\frac{\left(x+1\right)^2}{2}=882\)
\(\Leftrightarrow\left(x+1\right)^2=1764\)
\(\Leftrightarrow\orbr{\begin{cases}x+1=42\\x+1=-42\left(loaivix>0\right)\end{cases}}\)
\(\Leftrightarrow x=41\)
Vậy
( chỗ kia ghi là loại vì x >0 )
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