The answer is:
$\cos(1250\pi t)$ and $\cos(21250\pi t)$
I’m not able to verify.
My understanding is that when you periodically increase $t$ by $1/10$ ($10$ here is the frequency, so $1/10$ is time period) from $0$ to the signal $\cos(1250\pi t)$, you should get $x(n)=\cos(n\pi /8)$.
However, $\cos(1250\pi (1/10))$ is not same as $\cos((1)\pi /8)$.
So I would like the verification and what's wrong with my reasoning? Any help is appreciated.