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anonymous

  • one year ago

Find an exact value. cos 165°

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  1. Nnesha
    • one year ago
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    whats two number you can add to get 165? and those two number suppose to be on the unit circle

  2. Nnesha
    • one year ago
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    then use formula \[\large\rm cos(a+b)=\cos a \times \cos b - \sin a \times \sin b\]

  3. anonymous
    • one year ago
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    90 & 75 ?

  4. Nnesha
    • one year ago
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    well 75 is not on the unit circle :/

  5. Nnesha
    • one year ago
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    |dw:1438365794651:dw|

  6. anonymous
    • one year ago
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    120 + 45

  7. Nnesha
    • one year ago
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    30+135 40+120 225-60 for this u have to use cos(a-b)=cos a times cos b + sin a times sin b

  8. Nnesha
    • one year ago
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    perfect!

  9. Nnesha
    • one year ago
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    so \[\huge\rm cos(45+120)=\cos 45 \cos 120 - \sin 45 \sin 120\]

  10. anonymous
    • one year ago
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    okay, i see. what do i do from there?

  11. Nnesha
    • one year ago
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    so \[\large\rm cos(45+120)=\cos 45 \cos 120 - \sin 45 \sin 120\] now use the unit circle cor exact value of cos and sin cos 45 =? cos 120 =? sin 45=? sin 120 =? plugin their exact values

  12. anonymous
    • one year ago
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    cos 45 = (radical)2 / 2 cos 120 = -1/2 sin 45 = (radical) 2 /2 sin 120 = (radical) 3 /2 is that right?

  13. Nnesha
    • one year ago
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    \[\frac{ \sqrt{2} }{ 2 } \times \frac{ -1 }{ 2 } - \frac{ \sqrt{2} }{ 2 } \times \frac{ \sqrt{3} }{ 2}\] solve

  14. Nnesha
    • one year ago
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    yes that's right

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