Futuredoctr said:
So I'm reading my kaplan books (and others) and for example snell's law ( or any thing with a trig function) will come up and Ill derive it down (because after all I do have all equations memorized ) and I'll get something like Sin@=.3/1.8 (@=theta) and then the next thing I know the answer reads @=9.5 degrees. How do I do that? I believe its inverse sin, but in my head, come on??
Good question, but the answer may be unsatisfying: you don't have to be able to do this on actual MCAT questions. All you would need to be able to do, at the very most, on a problem like the one you quoted is to see that sin(theta) is (a lot) less than 0.5, the sin of 30 degrees, so the angle is also (a lot) less than 30 degrees. That'll be enough to choose the answer using process of elimination.
So, here's the general aproach to MCAT questions that ask for an angle as an answer. First, the
only angles you need to know anything about are 30, 45, and 60 degrees (plus things like 0 and 90, plus equivalent angles like 135 [which is the same as 45]). Moreover, you don't need to know them with any precision: on MCAT physics questions, one significant figure is plenty. This means that for 30 degrees, sine is 0.5 and cosine is 0.9; for 60 degrees these two are reversed, and for 45 degrees the sine and cosine are each 0.7. (Warning: MCAT chemistry questions sometimes do require more than one significant figure, but there's no trig needed for them.)
How, then, do you answer questions whose answers are other than these? Glad you asked. The rule is this:
angular answers to MCAT problems can only be angles you know about, plus angles that are actually discussed in the question or the passage, unless only one of the four answer choices is possible. In other words, any answer choice that is an angle that you don't know anything about (i.e., haven't memorized the sine and cosine of) and that isn't listed in the passage, cannot be the answer unless all other choices are obviously wrong.
For the problem listed, either they gave you an abbreviated trig table listing, among other angles, 9.5 degrees, or that was an angle that was discussed in the passage, say an initial angle or an experimental value, or all the other choices were 30 degrees or more (or 0). No, that probably wasn't the case in your practice material, but on the MCAT, it will be so.
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