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kenneyfamily

  • 3 years ago

if cos A= 0.8 and 270 < A < 360, find the exact value of sin2A a)0.28 b)0.96 c)-0.96 d)-0.6

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  1. jim_thompson5910
    • 3 years ago
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    Hint: sin(2A) = 2*sin(A)*cos(A) So you need to find the sin(A) first using the value of cos(A)

  2. kenneyfamily
    • 3 years ago
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    hmm how would i do that ?

  3. jim_thompson5910
    • 3 years ago
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    Using the idea cos^2 + sin^2 = 1

  4. kenneyfamily
    • 3 years ago
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    so .6

  5. jim_thompson5910
    • 3 years ago
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    but it's negative because we're in quadrant IV (sine is negative here)

  6. jim_thompson5910
    • 3 years ago
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    so sin(A) = -0.6

  7. jim_thompson5910
    • 3 years ago
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    now use sin(2A) = 2*sin(A)*cos(A)

  8. kenneyfamily
    • 3 years ago
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    -.96?

  9. jim_thompson5910
    • 3 years ago
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    yep

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