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anonymous

  • 5 years ago

If both x and y are in quadrant IV, and sin x = -2/3 and cos y = 1/4. Find cos (x-y)

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  1. anonymous
    • 5 years ago
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    cosxcosy+sinxsiny

  2. anonymous
    • 5 years ago
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    cos( x-y)= cos x cosy+ sinx siny

  3. anonymous
    • 5 years ago
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    sin x= -2/3 cox x =sqrt(1 +4/9)=sqrt(13)/3

  4. anonymous
    • 5 years ago
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    oh sorry

  5. anonymous
    • 5 years ago
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    cosx = sqrt(1-4/9)= sqrt(5)/3

  6. anonymous
    • 5 years ago
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    cosy =1/4 siny =- sqrt(1-1/16)=sqrt(15)/4

  7. anonymous
    • 5 years ago
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    put the values in formula

  8. anonymous
    • 5 years ago
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    ok thanks....another questions is to find sin (x+y) with the same variables... can you help me get started on that one also?

  9. anonymous
    • 5 years ago
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    oops, once would have been enough

  10. anonymous
    • 5 years ago
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    sin(x+y)= sinxcosy-cosxsiny

  11. anonymous
    • 5 years ago
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    values are same

  12. anonymous
    • 5 years ago
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    thank you

  13. anonymous
    • 5 years ago
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    so for cos (x-y) would it be: (√5/3)(1/4)+(-2/3)(√15/4)=(√5/12)+(-2√15/12)= √5-2√15/12

  14. anonymous
    • 5 years ago
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    siny is negative in fourth quadrant sin y =-sqrt(15)/4

  15. anonymous
    • 5 years ago
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    ok so it would be √5+2√15/12

  16. anonymous
    • 5 years ago
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    for sin (x+y) would it be (-2/3)(1/4)-(√5/3)((√15/4)= -2/12-√75/12=-2-5√3/12 are my negatives and positives right?

  17. anonymous
    • 5 years ago
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    u again missed that siny is negative

  18. anonymous
    • 5 years ago
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    -2/12+√75/12

  19. anonymous
    • 5 years ago
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    for sin (x+y) would it be (-2/3)(1/4)-(√5/3)((√15/4)= -2/12-√75/12=-2-5√3/12 are my negatives and positives right?

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