SAT Subject Test Mathematics Level 2

COTANGENT, SECANT, AND COSECANT

The answer is (E), but the above method is much longer, more involved, and more open to
calculator error than necessary. The best way to answer this question is to recognize the
relationship between what’s given and what’s asked for. Answering the question involves just one
quick calculation if you remember the relevant identity:

cos2A   =   cos^2 A −   sin^2 A

So the given cos is the same as the denominator of the expression you’re solving for:

So the only calculating you need to do is this: 19 ÷ 7 ≈ 2.71.

So it can come in handy to know lots of trigonometric identities. You don’t absolutely have to know
the double-angle and half-angle identities—there’s usually a way around them—but you’ll be better
equipped to work quickly and efficiently if you do know them.

LEVEL 2 IDENTITIES

Functions   of  Sums