# 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!

Algebra ->  -> 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!       Log On

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 Click here to see ALL problems on Trigonometry-basics 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(1132)   (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* =