Posted by John on Monday, February 10, 2014 at 8:08pm.
Show that
cot((x+y)/2)=(sin(x)sin(y))/(cos(x)cos(y))
for all values of x and y for which both sides are defined.

Precalculus  Steve, Monday, February 10, 2014 at 8:34pm
using the halfangle formulas,
sin(x)sin(y) = 2 cos((x+y)/2)sin((xy)/2)
cos(x)cos(y) = 2sin((x+y)/2)sin((xy)/2)
tada!

Precalculus  John, Monday, February 10, 2014 at 9:03pm
Wow, I tried that but I messed up signs! Thanks!

Precalculus  John, Monday, February 10, 2014 at 9:09pm
Oops I meant sum and difference

Precalculus  Steve, Tuesday, February 11, 2014 at 12:27am
No, I meant sum and difference. I started out trying the halfangle for tangent, but got bogged down. Then I saw the sums on the right and went the easy way.
Answer This Question
Related Questions
 algebra  Can someone please help me do this problem? That would be great! ...
 Trigonometry  Identities and proof  Show that cot((x+y)/2) =  (sin x  sin y...
 Trigonometry  Please review and tell me if i did something wrong. Find the ...
 TRIG!  Posted by hayden on Monday, February 23, 2009 at 4:05pm. sin^6 x + cos^6...
 tigonometry  expres the following as sums and differences of sines or cosines ...
 Mathematics  Trigonometric Identities  Let y represent theta Prove: 1 + 1/tan^...
 Math (Trig)  sorry, another I can't figure out Show that (1cot^2x)/(tan^2x1)=...
 Trigonometry  Hello all, In our math class, we are practicing the trigonometric...
 math  Simplify the trigonometric function sin^4xcos^4x cos^2&#...
 math  Prove that for all real values of a, b, t (theta): (a * cos t + b * sin t...
More Related Questions