Friday

January 30, 2015

January 30, 2015

Posted by **Kimmie** on Thursday, January 28, 2010 at 10:14pm.

cos B = -12/13 when Pi<B<3Pi/2, then what is the value of sin(a+b)?

I don't get the question... Help appreciated.

- pre-calculus -
**Reiny**, Thursday, January 28, 2010 at 10:27pmmake two separate diagrams,

one will be the 3,4,5 right-angled triangle,

the other will be the 5,12,13 right-angled triangle

given sin a = 3/5 and a is in the II quadrant, so cos a = -4/5

given cos B = -12/13 and B is in III, so

sin B = - 5/13

now you have to know the expansion for

sin(a+b) = sina cosb + cosa sinb

=(3/5)(-12/13) + (-4/5)(-5/13) = -16/65

- pre-calculus -
**Kimmie**, Thursday, January 28, 2010 at 10:57pmThanks!

**Answer this Question**

**Related Questions**

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

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 ...

Math - Calculus - The identity below is significant because it relates 3 ...

Mathematics - Trigonometric Identities - Let y represent theta Prove: 1 + 1/tan^...

algebra - Can someone please help me do this problem? That would be great! ...

Math - Test for symmetry with repsect to Q=pi/2, the polar axis, and the pole. ...

Math - Test for symmetry with repsect to Q=pi/2, the polar axis, and the pole. r...

trig - Reduce the following to the sine or cosine of one angle: (i) sin145*cos75...

Calculus 12th grade (double check my work please) - 1.)Find dy/dx when y= Ln (...