SOLUTION: Using the angle difference identity to find the exact value of cos225. I have come up with (-sqrt2)/2. Is this correct? Please help!

Question 744305: Using the angle difference identity to find the exact value of cos225. I have come up with (-sqrt2)/2. Is this correct? Please help!

Answer by fcabanski(1391) (Show Source): You can put this solution on YOUR website!
Use the sum and difference identities to express the trig functions in terms of the functions most people memorize (30, 45, 60, 90, 180, 270, 360).

cos(A+B) = cosA*cosB - sinA*sinB
cos(225) = cos(180+45) = cos(180)*cos(45) - sin(180)*sin(45) = -1* - 0* =

RELATED QUESTIONS
Find the exact value of cos225� using 2 different formulas. Please note: I tried using (answered by stanbon)

Use the angle sum or difference identity to find the exact value of cos195... (answered by Edwin McCravy)

find the exact value of tan315 using a sum or difference... (answered by lwsshak3)

The problem is asking me to use the angle sum or difference identity to find the exact... (answered by lwsshak3)

I have tried so many times to solve the problem Find the exact value of sin (x/2) =... (answered by Alan3354)

find the exact value using a double angle identity... (answered by lwsshak3)

find the exact value using a double angle identity... (answered by ikleyn,greenestamps)

Using a the half angle identity, find the exact value of sin22.5 degrees (answered by lwsshak3,Alan3354)

Using a sum or difference identity, write the following as an expression involving... (answered by lwsshak3)