Friday

February 27, 2015

February 27, 2015

Posted by **MIK** on Thursday, May 17, 2012 at 4:43pm.

- trig -
**Reiny**, Thursday, May 17, 2012 at 6:19pmsin a = 15/17 , with a in I, so cos a = 8/17

cos b = 4/5, with b in IV, then sin b = -3/5

cos(a+b) = cosa cosb - sina sinb

= (8/17)(4/5) - (15/17)(-3/5)

= (32 + 45)/85

= 77/85

**Answer this Question**

**Related Questions**

math - How would you establish this identity: (1+sec(beta))/(sec(beta))=(sin^2(...

pre calc - suppose beta is an angle in the second quadrant and tan beta=-2. ...

trig - evaluate the following in exact form, where the angeles alpha and beta ...

trig - verify the identity: sec(beta)+ tan (beta)= cos(beta)/ 1-sin(beta)

Trigonometry - Find the exact value of tan2(Beta) if sin(Beta) = 5/13 (Beta in ...

Trigonometry - Find the exact value of tan2(Beta) if sin(Beta) = 5/13 (Beta in ...

Math - Given that sin alpha=4/sqrt65, pi/2<alpha<pi, and cos beta=-3/...

Trigonometry - Prove that tan (Beta) sin (Beta) + cos (Beta) = sec (Beta) Please...

Pre-Calculus - If sin(theta)=15/17 and cos(beta)=(-5/13 (both theta and beta are...

Pre Calc. - Use the sum or difference identity to find the exact value of sin255...