Math

Use the given information to evaluate cos (a+b). Sin a = -7/25, cot b = -8/15. Neither a nor b are in quadrant IV. exact answers only. No decimals.

  1. 👍 0
  2. 👎 0
  3. 👁 69
  1. since the sine is negative in III or IV and the cotangent is negative in II or IV, and we are told that neither is in IV
    a must be in III and b must be in II

    sin a = -7/25, a in III
    cos a = -24/25

    cot b = -8/15 , b in II
    tan b = -15/8
    sinb = 15/17
    cosb = -8/17

    cos(a+b)
    = cosa cosb - sina sinb
    = (-24/25)(-8/17) - (-7/25)(15/17)
    = 297/425

    1. 👍 0
    2. 👎 0
    posted by Reiny

Respond to this Question

First Name

Your Response

Similar Questions

  1. algebra

    Can someone please help me do this problem? That would be great! Simplify the expression: sin theta + cos theta * cot theta I'll use A for theta. Cot A = sin A / cos A Therefore: sin A + (cos A * sin A / cos A) = sin A + sin A = 2

    asked by Valerie on February 18, 2007
  2. Trigonometry

    Please review and tell me if i did something wrong. Find the following functions correct to five decimal places: a. sin 22degrees 43' b. cos 44degrees 56' c. sin 49degrees 17' d. tan 11degrees 37' e. sin 79degrees 23'30' f. cot

    asked by Anon on January 1, 2011
  3. math

    Simplify the trigonometric function sin^4⁡x-cos^4⁡x cos^2⁡â-sin^2⁡â=1+2cos⁡â (1+cot^2⁡x )(cos^2⁡x )=cot^2⁡x cot^2⁡t/csc⁡t =(1-sin^2⁡t)/sin⁡t (Work on both sides!) sinècscè- sin^2⁡è=cos^2⁡è

    asked by Anonymous on June 4, 2015
  4. Trigonometry

    Hello all, In our math class, we are practicing the trigonometric identities (i.e., sin^2(x)+cos^2(x)=1 or cot(x)=cos(x)/sin(x). Now, we are working on proofs that two sides of an equation are equal (for example, sin(x)*csc(x)=1;

    asked by Timothy on February 25, 2008
  5. Pre-Calculus

    I don't understand,please be clear! Prove that each equation is an identity. I tried to do the problems, but I am stuck. 1. cos^4 t-sin^4 t=1-2sin^2 t 2. 1/cos s= csc^2 s - csc s cot s 3. (cos x/ sec x -1)- (cos x/ tan^2x)=cot^2 x

    asked by Anonymous on October 31, 2013
  6. Pre-Calculus

    Prove that each equation is an identity. I tried to do the problems, but I am stuck. 1. cos^4 t-sin^4 t=1-2sin^2 t 2. 1/cos s= csc^2 s - csc s cot s 3. (cos x/ sec x -1)- (cos x/ tan^2x)=cot^2 x 4. sin^3 z cos^2 z= sin^3 z - sin^5

    asked by Anonymous on October 31, 2013
  7. TRIG!

    Posted by hayden on Monday, February 23, 2009 at 4:05pm. sin^6 x + cos^6 x=1 - (3/4)sin^2 2x work on one side only! Responses Trig please help! - Reiny, Monday, February 23, 2009 at 4:27pm LS looks like the sum of cubes sin^6 x +

    asked by hayden on February 23, 2009
  8. Math (Trig)

    sorry, another I can't figure out Show that (1-cot^2x)/(tan^2x-1)=cot^2x I started by factoring both as difference of squares. Would I be better served by writing in terms of sine and cosine? Such as:

    asked by mtd on April 9, 2008
  9. trig

    it says to verify the following identity, working only on one side: cotx+tanx=cscx*secx Work the left side. cot x + tan x = cos x/sin x + sin x/cos x = (cos^2 x +sin^2x)/(sin x cos x) = 1/(sin x cos x) = 1/sin x * 1/cos x You're

    asked by Devon on May 7, 2007
  10. verifying trigonometric identities

    How do I do these problems? Verify the identity. a= alpha, b=beta, t= theta 1. (1 + sin a) (1 - sin a)= cos^2a 2. cos^2b - sin^2b = 2cos^2b - 1 3. sin^2a - sin^4a = cos^2a - cos^4a 4. (csc^2 t / cot t) = csc t sec t 5. (cot^2 t /

    asked by Anonymous on March 3, 2008

More Similar Questions