Question

\(\left\{{}\begin{matrix}u3+u6=-29\\u3.u11=25\end{matrix}\right.\)

Answer 1

Cấp số cộng hay cấp số nhân vậy bạn ? 

Answer 2

thiếu đề bài .

Answer 3

Uây chào bro, lâu ko gặp :)

\(u_3+u_6=-29\Leftrightarrow u_1+2d+u_1+5d=-29\)

\(\Leftrightarrow2u_1+7d=-29\left(1\right)\)

\(u_3.u_{11}=25\Leftrightarrow\left(u_1+2d\right)\left(u_1+10d\right)=25\)

\(\Leftrightarrow u_1^2+12u_1d+20d^2=25\left(2\right)\)

\(\left(1\right),\left(2\right)\Rightarrow\left\{{}\begin{matrix}2u_1+7d=-29\\u_1^2+12u_1d+20d^2=25\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}u_1=...\\d=....\end{matrix}\right.\)