# Expand Using Sum divide Difference Formulas cos((two pi) divide three)

Expand Using Sum/Difference Formulas cos((2pi)/3)
The angle is an angle where the values of the six trigonometric functions are known. Because this is the case, Sum to keep the value the same.
Use the sum formula for cosine to Clarify the expression. The formula states that .
The exact value of is .
Clarify .
Use the reference angle by calculating the angle with equivalent triginometric values in the Initially quadrant. Should be rewritten the expression as a negative one since cosine is negative in the 2nd quadrant.
The exact value of is .
The exact value of is .
Simplify .
Apply the reference angle by finding the angle with equivalent trig values in the first quadrant.
The exact value of is .
Clarify each term.
First, multiply by .
First, multiply by .