Find the exact value of the following expression without usi

Find the exact value of the following expression without using a calculator. cos 5 pi/3 cos 5 pi/3 = (Simplify your answer, including any radicals. Use integers or fractions for any numbers in the expression.)

Solution

cos(5pi/3) = cos(2pi - pi/3)

cos(2pi-theta)=cos theta

Therefore cos(2pi - pi/3) = cos (pi/3)=1/2