Trig question

[RandyJ 10+ year member]

Pain in my *** studying for a test

Anywhoo, simplify this, without the use of a calculator. I can tell you what you should get, tell me how I get it please.

cos(2sqrt5/5 + sqrt5/3) = cos(2sqrt5/5)cos(sqrt5/3)-sin(2sqrt5/5)sin(sqrt5/3)

book gives (10-2sqrt5)/15

I see where all the figures are coming from, but cannot put it all together

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[RandyJ 10+ year member]

Oopp, wait, i think I foudn the problem. Let me try using the tan(u-v) identity.

 

[RandyJ 10+ year member]

nvmd, book asks for the cos(u+v) //content.invisioncic.com/y282845/emoticons/crap.gif.7f4dd41e3e9b23fbd170a1ee6f65cecc.gif

 

[bibby 5,000+ posts]

that problem made my head hurt reading it.

 

[RandyJ 10+ year member]

that problem made my head hurt reading it.

Sorry, I cannot find the special combination of keys to give the square root symbol:crap:

 

[RandyJ 10+ year member]

Eh?