Really stuck with this problem, I need help with this asap.

To find cos(a-B), I'm supposed to use:

tan a = 4/3, with a in quadrant III

cos B = 12/13, with B in quadrant IV

  • $\begingroup$ Do you know that $cos(A-B)=cosAcosB+sinAsinB$? $\endgroup$ – Indrayudh Roy May 13 '14 at 10:28
  • $\begingroup$ Of course, I started by using that formula, but I'm still having trouble. $\endgroup$ – user139473 May 13 '14 at 10:48


I have shown the relevent identities . I hope this helps answer your question.


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