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anonymous

  • 5 years ago

Use identities (no calculators) to find the exact value for (sin 38)(sin 112) -( cos 38)(cos 112).

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  1. anonymous
    • 5 years ago
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    same trick as before. this is the addition angle formula for cosine{ \[cos(a+b)=cos(a)cos(b)-sin(a)sin(b)\]

  2. anonymous
    • 5 years ago
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    here \[a=38,b=112, a+b=150\]

  3. anonymous
    • 5 years ago
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    well on careful inspection i see that this is it's negative, but that is ok \[cos(150)=-\frac{\sqrt{3}}{2}\] so your answer here is \[\frac{\sqrt{3}}{2}\]

  4. anonymous
    • 5 years ago
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    Why does the negative turn to a positive?

  5. anonymous
    • 5 years ago
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    oh because the "addition angle" formula is not the one written in the question. it is its negative

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