SOLUTION: How do you find the cos of 55 degrees using the sum and difference identity? cos (x + y) = (cos x) (cos y) - (sin x) (sin y) and cos (x - y) = (cos x) (cos y) +

Algebra.Com
Question 261459: How do you find the cos of 55 degrees using the sum and difference identity?
cos (x + y) = (cos x) (cos y) - (sin x) (sin y) and
cos (x - y) = (cos x) (cos y) + (sin x) (sin y)
I can't find 2 angles that add or subtract to get 55.
Ex: 315 - 270 = 45 degrees, not 55
Answer by Edwin McCravy(20060)   (Show Source): You can put this solution on YOUR website!
There aren't any special angles that will give 55°.
I suspect that the problem was a book typo, and
should have been 75°, perhaps, which could have
geen gotten with 45°+30°

Edwin
RELATED QUESTIONS

Verify the identity. (cos(x) - cos(y))/(sin(x) + sin(y)) + (sin(x) - sin(y))/(cos(x) + (answered by solver91311)
Suppose sin x = 5/7 cos x > 0, sin y = − 1/5 and cos y < 0. Then cos x = cos... (answered by lwsshak3)
Verify the identity. cos (x - y) - cos (x + y) = 2 sin x sin y (answered by solver91311)
Verify the identity. cos (x - y) - cos (x + y) = 2 sin x sin y (answered by lynnlo)
Verify the identity. cos (x - y) - cos (x + y) = 2 sin x sin y (answered by lynnlo)
Suppose sin x = 1/7 cos x > 0, sin y = −2/5 and cos y < 0. Then cos x = cos y (answered by ewatrrr)
Suppose sin x = 1/7 cos x > 0, sin y = −2/5 and cos y < 0. Then cos x = cos y (answered by stanbon)
Suppose sin x = 1/7 cos x > 0, sin y = −2/5 and cos y < 0. Then cos x =... (answered by lwsshak3)
Suppose sin x =2/7,cos x > 0, sin y = − 2/5 and cos y < 0. Then cos x= cos y= Find (answered by CPhill)