Sunday

December 21, 2014

December 21, 2014

Posted by **Anonymous** on Friday, July 9, 2010 at 2:23pm.

- Trig -
**Reiny**, Friday, July 9, 2010 at 2:25pmhave you come across this formula ?

cos(A+B) = cosAcosB - sinAsinB

your expression matches this

Cos(21)cos(9)-sin(21)sin(9)

= cos(21+9)

= cos30

= √3/2

**Answer this Question**

**Related Questions**

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 ...

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

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

Precal - I do not understand how to do this problem ((sin^3 A + cos^3 A)/(sin A...

trig - The expression 4 sin x cos x is equivalent to which of the following? (...

trig - it says to verify the following identity, working only on one side: cotx+...