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College Trigonometry, 2011a

College Trigonometry, 2011a

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860 Foundations of <strong>Trigonometry</strong><br />

a reciprocal identity to rewrite the secant as cosine. The x-coordinates of the intersection<br />

1<br />

points of y = and y = 4 verify our answers.<br />

(cos(x)) 2<br />

y = cos(3x)<br />

sin(3x)<br />

and y =0 y =<br />

1<br />

cos 2 (x)<br />

and y =4<br />

5. The equation tan ( )<br />

x<br />

2 = −3 has the form tan(u) =−3, whose solution is u =arctan(−3)+πk.<br />

Hence, x 2<br />

=arctan(−3) + πk, sox = 2 arctan(−3) + 2πk for integers k. To check, we note<br />

tan<br />

( )<br />

2 arctan(−3)+2πk<br />

2<br />

= tan (arctan(−3) + πk)<br />

= tan (arctan(−3)) (the period of tangent is π)<br />

= −3 (See Theorem 10.27)<br />

To determine which of our answers lie in the interval [0, 2π), we first need to get an idea of<br />

the value of 2 arctan(−3). While we could easily find an approximation using a calculator, 5<br />

we proceed analytically. Since −3 < 0, it follows that − π 2<br />

< arctan(−3) < 0. Multiplying<br />

through by 2 gives −π

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