Dear Hexin,

 Please consult

https://sites.math.rutgers.edu/~zeilberg/Hist21/q6S.pdf

for the full solutions.

You got 6 points (out of 10).

You started #4 correctly, but then completely messed up. By luck you got the right answer for one of the roots. The other two roots are also correct, but
you did not explain.


 Best wishes,

   Dr. Z.