Sunday

February 1, 2015

February 1, 2015

Posted by **jj reddick** on Sunday, October 24, 2010 at 11:23pm.

- trig -
**Reiny**, Sunday, October 24, 2010 at 11:31pmyou should recognize the 3,4,5 and the 5,12, 13 right-angled triangles, so

if sinx = 4/5, then cosx = -3/5 in II

if cosy = -1213, then siny = 5/13 in II

to have this type of question, you must also have come across the expansions for sin(A+B), cos(A-B), etc.

I will do cos(x-y)

cos(x-y) = cosx cosy + sinx siny

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

= 56/65

**Answer this Question**

**Related Questions**

TRIG! - Posted by hayden on Monday, February 23, 2009 at 4:05pm. sin^6 x + cos^6...

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

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

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

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

trig - suppose sin(x)=5/6, and x is in the first quadrant. Determine cos(x), sin...

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

pre-cal - Simplify the given expression........? (2sin2x)(cos6x) sin 2x and cos ...