Thursday

December 18, 2014

December 18, 2014

Posted by **Michael** on Sunday, August 30, 2009 at 10:03pm.

- trig -
**Reiny**, Monday, August 31, 2009 at 12:27amsince the = and + sign are on the same key, I will assume cos(a=b) is a typo and you meant

cos(a+b)

cos(a+b) = cos(a)cos(b) - sin(a)sin(b)

since a is in II and sin(a) = 3/5, cos(a) = -4/5

since b in in I and cos(b) = 5/13, sin(b) = 12/13

so cos(a+b) = (4/5)(5/13) - (3/5)(12/13)

= (-20-36)/65

= -56/65

**Answer this Question**

**Related Questions**

trig - how do you work find sin (a-B)beta sign. sin a = 12/13,a lies in quadrant...

trig - Find sin è/2 for cos è = 1/4 and è lies in Quadrant I.

math - sin a=3/5, a lies on quadrant 1 and sin b=5/13, b lies on quadrant 2. ...

trig - Given that sin = 3/5 and lies in quadrant II, find the following value. ...

maths - Angle a lies in the second quadran and angle b lies in the third ...

trig - angle x lies in quadrant 3 and cos(x)=-.6. Find cos(3pi/2-x)

Pre-calc/Trig - If cot(a)=3 and sin(b)= (15/17) where a being alpha lies in ...

trig - can someone please help me with this problem. i'm doing my review right ...

mth, trig - Given cos a=-7/25 in quadrant II , and sin b=-12/13, in quadrant IV...

Trig - Find cos(s+t) if cos s= -1/2 and sin t= 3/5, s and t are in quadrant II. ...