[MOVED] Suppose cos(x+y) = 1/4 and cos x cos y = 5/24.

[FMMurphy]

Suppose cos(x+y) = 1/4 and cos x cos y = 5/24. What is the value of cos (x-y)?

(cos (x+y) = cos x cos y - sin x sin y, and cos (x-y) = cos x cos y + sin x sin y

 

[stapel]

Where are you stuck? You've plugged the given values for cos(x + y) and cos(x)cos(y) into the first identity and found the value of sin(x)sin(y). Then you've plugged the values for cos(x)cos(y) and sin(x)sin(y) into the second identity, simplified, and... then what?

Please be specific. Thank you.

Eliz.

 

[i'madodo]

Try using the identity, cos(x+y)=cos(x)cos(y)-sin(x)sin(y) into the first equation