Typo in 2.5 Q23

[Jerry Qinghui Yu]

Hello, professor, there is a typo that reads

$\frac{x}{dt} = âˆ′\alpha xy$

Should be

$\frac{dx}{dt} = -\alpha xy$

Also could you fix the link of "Test 1" on course page? It links to last year's.

[Victor Ivrii]

Fixed both. Thanks!