## bridgetx516x 2 years ago Find cos(x+y) for cos x =-4/5 ans sin y = 5/13 with x and y being in quadrant 2.

1. bridgetx516x

this is what i have got so far..|dw:1364147163106:dw|

2. bridgetx516x

that would give me an answer of .9995 which is not an option a. .51 b. .97 c. -.51 d. -1.72 e. None of the above. is the answer E or have I done something wrong?

3. harsimran_hs4

no answer is not e you have applied totally wrong concept cos(x + y) where x and y are angles x is not -4/5 but cos x = -4/5 use : cos(x + y) = (cosx)*(cosy) - (sinx) * (siny)

4. bridgetx516x

i just tried that and still didnt get and an answer. I did: cos(-4/5) Cos(-12/13) - sin(3/5) sin(5/13) (.99)(.99)- (.01)(.006) (.99)-(.00007) = .999702 @harsimran_hs4

5. harsimran_hs4

you are doing the same mistake please have a look at the above comment MIND IT: X IS ANGLE AND NOT -4/5 COS X = -4/5

6. bridgetx516x

oh alright. but i did it and got -.97 and an answer

7. bridgetx516x

just kidding I got .51

8. harsimran_hs4

so you are done or still any doubt?

9. bridgetx516x

yes i am, thank you!

10. harsimran_hs4

cool :)