What is the inverse cosine of 1/3?

1 Answer
Nov 29, 2015

theta~~70.53^@, 289.47^@

Explanation:

Since 1/3 is not a ratio we can find in a special triangle, we must use a calculator:

costheta=1/3
theta=cos^-1(1/3)
theta~~70.53^@

However, since cosine is also positive in quadrant 4 according to the CAST rule, there is a second answer:

theta=360^@-70.53^@
theta~~289.47^@