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felicia888

  • 2 years ago

Find the exact value of the expression using the provided information: cos A = -1/6 and cos B = -3/5 pi<A<3pi/2 and pi<B<3pi/2

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  1. felicia888
    • 2 years ago
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    Please explain, I'm lost on this one

  2. felicia888
    • 2 years ago
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    Maybe using Sum or Difference Identity: cos(A+B) = cos A cos B - sin A sin B?

  3. chihiroasleaf
    • 2 years ago
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    what is the question?

  4. Mertsj
    • 2 years ago
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    You say to find the exact value of the expression and then you don't give the expression.

  5. felicia888
    • 2 years ago
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    sorry, cos(A+B)

  6. felicia888
    • 2 years ago
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  7. Mertsj
    • 2 years ago
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    cos(A+B)= cosAcosB-sinAsinB

  8. felicia888
    • 2 years ago
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    That's as far as I've gotten I'm not sure on how to use the formula

  9. Mertsj
    • 2 years ago
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    You know that both A and B are 3rd quadrant angles. That is given. So the sin and cos of both angles must be negative.

  10. Mertsj
    • 2 years ago
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    |dw:1352460203985:dw|

  11. Mertsj
    • 2 years ago
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    |dw:1352460347694:dw|

  12. Mertsj
    • 2 years ago
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    Use those values in the formula for cos (A+B)

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