Question

mn giúp e gấp câu 30 với ạ em cảm ơn

Answer 1

30:

\(\Leftrightarrow\left\{{}\begin{matrix}u1+q+u1+3q+u1+5q=39\\u_1^3+\left(u_1+q\right)^3=82\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}u_1+3q=13\\u_1^3+\left(u_1+q\right)^3=82\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}q=\dfrac{13}{3}-\dfrac{1}{3}u_1\\u_1^3+\left(\dfrac{2}{3}u_1+\dfrac{13}{3}\right)^3=82\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}q=4\\u_1=13-3q=1\end{matrix}\right.\)