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anonymous

  • 5 years ago

write the given expression as the cosine of an angle: cos(70°)cos(65°)-sin(70°)sin(65°) a)cos(65°) b)cos(135°) c)cos(5°) d)cos(70°) e)cos(-130°)

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  1. anonymous
    • 5 years ago
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    Know that cos(x)=sin(90-x) likewise sin(x)=cos(90-x)

  2. anonymous
    • 5 years ago
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    ya I got that.... just don't know where to go from there

  3. anonymous
    • 5 years ago
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    so just change sin() into cos()

  4. anonymous
    • 5 years ago
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    ok but thats still not one of the choices for an answer

  5. anonymous
    • 5 years ago
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    cos(70)cos(65)-cos(20)cos(35)

  6. anonymous
    • 5 years ago
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    When you solve this you should get numerical answer of about -.625 Take arcos of this then you will get 128. which is close to 135

  7. anonymous
    • 5 years ago
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    ok... thanks

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