Posted by **rick** on Tuesday, February 26, 2008 at 1:24pm.

If sin = 4/5 with A in QII, and sin B = -3/5 with B in QIV find cos(A-B)

- trig -
**^Quen^**, Tuesday, February 26, 2008 at 8:46pm
cos(A-B)= cosAcosB+sinAsinB

If sinA = 4/5 in QII

draw you triangle in QII, and find the third side.

The third side is 3. (Do the same thing for sin B= -3/5

Plug in:

cosAcosB-sinAsinB

=(-3/5)*(4/5)+(4/5)*(-3/5)

=(-12/25) -(-12/25)

=-24/25

- trig -
**Anonymous**, Tuesday, September 11, 2012 at 7:59pm
53. the longest side is 55 cm. find the length of the shortest side

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