<p>Hi. I was doing some math problems on Barron's and one of the questions was:</p>
<p>If f (r, theta) = r cos (theta), then f (2, 3) =</p>
<p>The answer the book gave is -1.98 and you had to use the radian mode.
But, I didn't think that the question implied in any way that I had to use the radian mode (which led me to get 2.00 as answer by using the degree mode, which also was one of the answer choices). And I also thought theta meant "use degree mode."</p>
<p>So, how can I know which mode to use on a problem?</p>
<p>Thanks</p>