\(\left\{{}\begin{matrix}u_2+u_5-u_4=10\left(1\right)\\u_3+u_6-u_5=20\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}u_2+u_5-u_4=10\\u_2.q+u_5.q-u_4.q=20\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}u_2+u_5-u_4=10\\q.\left(u_2+u_5-u_4\right)=20\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}u_2+u_5-u_4=10\\q.10=20\end{matrix}\right.\)
\(\Rightarrow q=2\)
\(\left(1\right)\Rightarrow u_1.q+u_1.q^4-u_1.q^3=10\)
\(\Leftrightarrow u_1.\left(q+q^4-q^3\right)=10\)
\(\Leftrightarrow u_1.=\dfrac{10}{\left(q+q^4-q^3\right)}=\dfrac{10}{2+2^4-2^3}=1\)
Vậy \(u_1=1;q=2\)
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