Friday

April 18, 2014

April 18, 2014

Posted by **Bryan** on Friday, March 19, 2010 at 4:42pm.

cos(4/5 - 5/13)

Is this what I would do?

- math -
**drwls**, Friday, March 19, 2010 at 4:48pmYour sin(x) fraction lacks a numerator

- math -
**Bryan**, Friday, March 19, 2010 at 4:51pmthe sine is 4/5 sorry!

- math -
**drwls**, Friday, March 19, 2010 at 8:13pmNo, that is not what you would do. Call the angles A and B.

For the angles you have chosen,

cos(x) = 3/5 and sin(y) = 12/13. You can prove that with the Pythagorean theorem, or sin^2 + cos^2 = 1. That will make the calculation easier.

Then use the identity:

cos(A-B) = cosA cosB + sinA sin B

= (3/5)(5/13) + (4/5)(12/13)

= (15 + 48)/65 = 63/65

**Related Questions**

Math - If sin(x) = /45 and cos(y) = 5/13 with both x and y terminating in ...

Please help!!!) - If sin(x) = /45 and cos(y) = 5/13 with both x and y ...

Math - If sin(x) = 4/5 and cos(y) = 5/13 with both x and y terminating in ...

Alg2/Trig - Find the exact value of the trigonometric function given that sin u...

Trig - Given: cos u = 3/5; 0 < u < pi/2 cos v = 5/13; 3pi/2 < v < ...

Math- Trig - 1. Determine the exact value of cos^-1 (pi/2). Give number and ...

Trig hep, please? Thank you! - 1. Find the exact value of sin(195(degrees)) 2. ...

Math!!! - angle x is in the second quadrant and angel y is in the first quadrant...

trigonometry - 5. If cot 2θ = 5/12 with 0 ≤ 2θ ≤ π...

math - Determine exact value of cos(cos^-1(19 pi)). is this the cos (a+b)= cos a...