Answer:
See below for answers and explanations
Step-by-step explanation:
<u>Problem 1</u>
To convert from polar to Cartesian coordinates, recall that
, thus, 
Therefore, C is the correct answer
<u>Problem 2</u>
Convert from polar to Cartesian coordinates:

Therefore, U is the correct answer
<u>Problem 3</u>
Since
, then
. Don't also forget to use the substitution
:

Therefore, B is the correct answer
<u>Problem 4</u>
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Therefore, A is the correct answer