\(\left\{{}\begin{matrix}u2-3u8=-20\\u_3\cdot u_4=24\end{matrix}\right.\)
=>\(\left\{{}\begin{matrix}u1+d-3\left(u1+7d\right)=-20\\u3\cdot u4=24\end{matrix}\right.\)
=>\(\left\{{}\begin{matrix}-2u1-20d=-20\\u3\cdot u4=24\end{matrix}\right.\)
=>\(\left\{{}\begin{matrix}u1+10d=10\\\left(u1+2d\right)\cdot\left(u1+3d\right)=24\end{matrix}\right.\)
=>\(\left\{{}\begin{matrix}u1=10-10d\\\left(10-10d+2d\right)\left(10-10d+3d\right)=24\end{matrix}\right.\)
=>\(\left\{{}\begin{matrix}u1=10-10d\\\left(-8d+10\right)\left(-7d+10\right)=24\end{matrix}\right.\)
=>\(\left\{{}\begin{matrix}u1=10-10d\\56d^2-150d+126=0\end{matrix}\right.\)
=>\(\left\{{}\begin{matrix}d\in\varnothing\\u1=10-10d\end{matrix}\right.\)
=>Không có số hạng đầu và công sai nào thỏa mãn yêu cầu đề bài
