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C-70 Appendix C<br />

EXAMPLE<br />

3 Values of Some Expressions Involving the Second Version<br />

of the Inverse Secant<br />

p<br />

You can show that Sec 1 2 3, Sec[Sec 1 (5)] 5, and Sec 1 (Sec 2 as in<br />

Example 1. However, Arcsec(12) the unique number in [0, p 3 ) 2<br />

5p<br />

whose secant is 12 3p 2 ) 3<br />

(p 2 , p]<br />

4 , not as in Example 1.<br />

4<br />

Note: Sec 1 x sec 1 x for x 1, but Sec 1 x 2p sec 1 x for x 1.<br />

EXAMPLE<br />

4 Evaluating Expressions Involving the Second Version of the Inverse Secant<br />

sin[Sec 1 ( 5 2)] 1215 as in Example 2(a). Or, by the previous note,<br />

œ„„ 55<br />

8<br />

~<br />

¨<br />

3<br />

y<br />

¨<br />

x<br />

8<br />

sin c Sec 1 a 5 2 bd sin c sec1 a 5 121<br />

bd <br />

2 5<br />

But, Sec 1 ( 3) is in ( p 2, p], sec 1 ( 3) is in [p, 3p and neither equals p.<br />

(Why?) So and in fact Z tan [sec 1 8<br />

tan[Sec 1 8<br />

Sec 1 8<br />

( 3) sec 1 2 ),<br />

8<br />

( 3),<br />

( 3)] ( 3)].<br />

To evaluate let u Sec 1 8<br />

tan[Sec 1 8<br />

( 3)],<br />

( 3) and let ũ be its reference angle.<br />

Then u is in ( p 2, p] and Sec u 8 3. Using the right triangle labeled in Figure E,<br />

we have<br />

opposite<br />

ũ <br />

Why is<br />

adjacent 155<br />

tan[Sec 1 8<br />

( 3)] tan u tan<br />

3 tan tan ˜?<br />

8<br />

Figure E<br />

Alternatively, using identities, sec u 8 3, so<br />

155<br />

tan u 2sec 2 u 1 2( 83) 2 1 <br />

3<br />

Why the negative<br />

square root?<br />

Exercises<br />

In each of these exercises the secant and the Secant are the restricted versions<br />

defined in this project, so the inverse secant and the inverse Secant are the corresponding<br />

inverse functions.<br />

1. Evaluate the following quantities:<br />

(a) sec 1 (0) (c) arcsec(1) (e) arcsec 12<br />

(b) sec 1 1 2132 (d) sec[sec 1 (10)] (f) sec 1 (sec 4)<br />

2. Evaluate the following quantities:<br />

(a) (b) sin[arcsec(5)] (c) tan3sec 1 7<br />

cos3sec 1 1 6 524<br />

1 3 24<br />

3. Evaluate the following quantities:<br />

(a) Sec 1 (1) (c) Arcsec(2) (e) Sec[Sec 1 (15)]<br />

(b) Sec 1 (Sec 2) (d) (f) tan3Sec 1 15<br />

sin3Sec 1 1 13 5 24<br />

1 7 24<br />

4. Prove<br />

Sec 1 x sec 1 x for x 1<br />

and<br />

Sec 1 x 2p sec 1 x for x 1<br />

5. Use the result in Problem 4 to show that<br />

tan3sec 1 8<br />

tan3Sec 1 8<br />

1 324 1 324 1553<br />

6. Explain why each of the following statements is true:<br />

(a) sec[Sec 1 (3)] 3<br />

(e) Sec 1 3sec1 4 324 4<br />

(b) sec[Sec 1 (3)] is undefined (f) sec 1 3Sec 3p<br />

(c) Sec[sec 1 (8)] 8 (g) sec 1 4 4 5p 3<br />

4<br />

(Sec 2) 2p 2<br />

(d) Sec[sec 1 (8)] is undefined

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