口算：\((x+2)(x+4)=80\) 2025-07-112025-07-11 易林 \[ \begin{align*} & 令t=x+3, \\ & 原式化为：(t-1)(t+1)=80 \\ & t^2 -1 =80 \\ & t^2 = 81 \\ & t = \pm9 \\ 即:x=-6,或x=12. \end{align*} \]