cos^-1( 7/14)

You should learn how to use the calculator here:cos^-1( 7/14)=60 degrees.

7/14 = 1/2

According to special angles table, cos \(60^{\circ}\) = \(\frac{1}{2}\)

\(\therefore cos^{-1}(\frac{7}{14})=60^{\circ}\)

Here is a special angles table: http://www.mathwords.com/t/trig_values_of_special_angles.htm