(\(x\) \(\times\) (\(x\) + 1)): 2 = 153
(\(x\) \(\times\) (\(x\) + 1)) = 153 \(\times\) 2
\(x\) \(\times\) (\(x\) + 1) = 306
\(x\)2 + \(x\) = 306
\(x^2\) + \(x\) - 306 = 0
\(x^2\) - 17\(x\) + 18\(x\) - 306 =0
\(x\) \(\times\) (\(x\) - 17) + 18 \(\times\) (\(x\) - 17) = 0
(\(x\) - 17)\(\times\) ( \(x\) + 18) = 0
\(\left[{}\begin{matrix}x-17=0\\x+18=0\end{matrix}\right.\)
\(\left[{}\begin{matrix}x=17\\x=-18\end{matrix}\right.\)
\(\text{#040911}\)
\(x\cdot\left(x+1\right)\div2=153\)
\(\Rightarrow x\cdot\left(x+1\right)=153\cdot2\)
\(\Rightarrow x\cdot\left(x+1\right)=306\)
\(\Rightarrow x^2+x=306\)
\(\Rightarrow x^2+x-306=0\)
\(\Rightarrow x^2+18x-17x-306=0\)
\(\Rightarrow\left(x^2+18x\right)-\left(17x+306\right)=0\\ \Rightarrow x\left(x+18\right)-17\left(x+18\right)=0\\ \Rightarrow\left(x-17\right)\left(x+18\right)=0\)
\(\Rightarrow\left[{}\begin{matrix}x-17=0\\x+18=0\end{matrix}\right.\\ \Rightarrow\left[{}\begin{matrix}x=17\\x=-18\end{matrix}\right.\\ \text{Vậy, x }\in\left\{-18;17\right\}.\)
\(x\left(x+1\right):2=153\)
\(x\left(x+1\right)=306\)
\(x^2+x=306\)
\(x=17;x=-18\)
\(\left[x\left(x+1\right)\right]:2=153\)
\(\Rightarrow\left[x\left(x+1\right)\right]=153.2\)
\(\Rightarrow x\left(x+1\right)=306\)
Vì \(306=17.18=\left(-7\right).\left(-18\right)\)
\(\Rightarrow x\in\left\{17;-18\right\}\)