Question

Find the exact value of sec 120°.

Answer 1

For this case we have that by definition:

$Sec (a) = \frac {1} {cos (a)}$

Then, we can rewrite the expression as:

$Sec (120) = \frac {1} {cos (120)}$

$cos (120) = cos (180-60) = - cos (60) = - \frac {1} {2}$

So:

$Sec (120) = \frac {1} {- \frac {1} {2}}\\Sec (120) = - 2$

Answer:

-2