Answer
$1.91$
Work Step by Step
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
$\sec^{-1}{(-3)}=\cos^{-1} {\left(\frac{1}{-3}\right)}\approx1.91$
