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

## Answer This Question

## Related Questions

- trig - If sin A= 1/4 and sin B= -1/2, with A in QII and B in QIV, find tan(A+B)
- TRIG! - Posted by hayden on Monday, February 23, 2009 at 4:05pm. sin^6 x + cos^6...
- trig - Reduce the following to the sine or cosine of one angle: (i) sin145*cos75...
- tigonometry - expres the following as sums and differences of sines or cosines ...
- Trig - Find sin(s+t) and (s-t) if cos(s)= 1/5 and sin(t) = 3/5 and s and t are ...
- Trig - Given: cos u = 3/5; 0 < u < pi/2 cos v = 5/13; 3pi/2 < v < ...
- Mathematics - Trigonometric Identities - Let y represent theta Prove: 1 + 1/tan^...
- algebra - Can someone please help me do this problem? That would be great! ...
- trig - If sin = -3/5 with A in QIV, find cos A/2
- trig - The expression 4 sin x cos x is equivalent to which of the following? (...

More Related Questions