<p>Write sin(x − (3π/2)) in terms of sin x and cos x. </p>
<p>how do you do this? that n is supposed to be pi. thanks</p>
<p>You know that sin(x) = cos((pi/2) - x); that’s a basic trigonometric identity. Apply it to the equation you have, and you can rewrite it as cos(2pi - x). The cosine function has a period of 2pi, so this is equivalent to cos(-x), and since the cosine function is even, you can drop the negative and end up with just cos(x).</p>
<p>you have to use the trig addition /subtraction formulas.
sin(a-b) =sin blah blah blah I forgot…</p>
<p>was this on the SAT reasoning test or what??</p>
<p>Nope, trig is not on SAT I test.</p>
<p>the sin(x±y) = sinxcosx ± cosysinx</p>
<p>so sin(x − (3π/2)) = (sinx)(cos(3pi/2)) - (cosx)(sin(3pi/2))
which is (sinx)(0) - (cosx)(-1)
which is cosx</p>
<p>where can I get a list of basic identities?</p>
<p>[List</a> of trigonometric identities - Wikipedia, the free encyclopedia](<a href=“http://en.wikipedia.org/wiki/List_of_trigonometric_identities]List”>List of trigonometric identities - Wikipedia)</p>
<p>you only really need to know adding subtracting doubling and halving sin cos and tan, and doubling you can derive really easily from adding, ie</p>
<p>sin(x+y) = sinxcosy + cosxsiny</p>
<p>sin(x+x) = sinxcosx + cosxsinx = 2sinxcosx</p>
<p>half angle identities are virtually nonexistent on the SAT and you can easily get by knowing only addition/subtraction</p>
<p>Oh, I have no idea why I didn’t say this, but this isn’t for ACT or SAT. I have a placement test to take calculus and I haven’t taken trig ( well sort of, its’ a long story) and I want to understand those rules before tomorrow at one. Wish me luck!</p>
<p>we made up songs for them in calc. sine: sin cos cos sin, cos: cos cos sin sin, with the sine the sign stays the same and (tan tan)/ 1 minus tantan <–to the tune of the can can</p>
<p>I passed! Thanks everyone for the help!</p>