Level:
Project ID:
1003097007
Accepted:
1
Clonable:
0
Easy:
0
Find the common difference of an arithmetic sequence \( \left\{a_n\right\}_{n=1}^{\infty} \), if the sum of the first seven terms is $42$ and $a_{10}=-4a_5$:
\[ \begin{aligned}
s_7&=42 \\
a_{10}&=-4a_5
\end{aligned} \]
\( -3 \)
\( 3 \)
\( 15 \)
\( 2 \)
\( -2 \)