Chapter 7 - Analytic Trigonometry - 7.2 The Inverse Trigonometric Functions (Continued) - 7.2 Assess Your Understanding - Page 458: 48

$1.91$

Note that $\sec {x}=\frac{1}{\cos{(x)}}$,. Hence, $\sec^{-1}{x}=\cos^{-1} {\left(\frac{1}{x}\right)}$. Use a calculator in radian mode and round the result to decimal places to obtain $\sec^{-1}{(-3)}=\cos^{-1} {\left(\frac{1}{-3}\right)}\approx1.91$