The problem is:
cos(-7pi/12)
I used the half angle formula to get: -(sqrt(3)-1)*sqrt(2)/(4)
Somehow or another the computer system isn't taking my answer.
Thanks for the help!
Here are the directions the computer system is still not taking it:
Use a sum or difference formula or a half angle formula to determine the value of the trigonometric functions. Give exact answers. Do not use decimal numbers. The answer should be a fraction or an arithmetic expression. If the answer involves a square root it should be enter as sqrt; e.g. the square root of 2 should be written as sqrt(2);
Thanks!