2. For the geometric sequence $\left\{a_{n}\right\}$ with all terms being real numbers, the sum of the first $n$ terms is $S_{n}$. If $S_{10}=10, S_{30}=70$, then $S_{40}$ equals $\qquad$ .
2. 150 or -200.
$\left\{a_{n}\right\}$ is a geometric sequence, then $S_{10}, S_{20}-S_{10}, S_{30}-S_{20}, S_{40}-S_{30}$ form a geometric sequence. $10\left(70-S_{20}\right)=\left(S_{20}-10\right)^{2}$, so $S_{20}=-20$ or $S_{20}=30$, therefore $S_{40}=150$, or $S_{40}=-200$.