PR math sat ii question

Archive SAT Subject Test Preparation
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<p>A full solution can be found here, post #8:
<a href=“http://talk.collegeconfidential.com/sat-subject-tests-preparation/1547837-how-hell-can-one-memorize-all-trig-formulas-math-iic.html[/url]”>http://talk.collegeconfidential.com/sat-subject-tests-preparation/1547837-how-hell-can-one-memorize-all-trig-formulas-math-iic.html&lt;/a&gt;&lt;/p&gt;

<p>My solution basically involved using some double-angle formulae to show that the original equation was equivalent to</p>

<p>(cos A - sin A)(sin 2A + 1) = 0</p>

<p>Hence cos A - sin A = 0 (choice B, e.g. let A = pi/4) or A = 3pi/4. Since these give different results for sin A - cos A, the correct answer is E) It cannot be determined.</p>