Question

tìm x

[ x * ( x + 1 ) ] : 2 = 153

Answer 1

\(\text{#040911}\)

\(\left[x\cdot\left(x+1\right)\right]\div2=153\\ \Rightarrow x\cdot\left(x+1\right)=153\cdot2\\ \Rightarrow x\cdot\left(x+1\right)=306\\ \Rightarrow x^2+x=306\\ \Rightarrow x^2+x-306=0\\ \Rightarrow x^2+18x-17x-306=0\\ \Rightarrow\left(x^2+18x\right)-\left(17x+306\right)=0\\ \Rightarrow x\left(x+18\right)-17\left(x+18\right)=0\\ \Rightarrow\left(x-17\right)\left(x+18\right)=0\)

\(\Rightarrow\left[{}\begin{matrix}x-17=0\\x+18=0\end{matrix}\right.\\ \Rightarrow\left[{}\begin{matrix}x=17\\x=-18\end{matrix}\right.\\ \text{Vậy, x }\in\left\{-18;17\right\}.\)