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rini94

  • 4 years ago

if the point P(-3/5,y) lies on the unit circle and P is in the third quadrant, what does y equal?

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  1. amistre64
    • 4 years ago
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    the unit circle is made of cos, sin coords

  2. MrYantho
    • 4 years ago
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    Since the x value is negative, we are talking left of the y-axis (Q2 or 3). We are told Q# so that means that our y-coord must also be negative. |dw:1331832229558:dw| Consider than creating a triangle by drawing a radius and drawing a line up to the x-axis

  3. amistre64
    • 4 years ago
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    sin^2 + cos^2 = 1 ; was my first impression :) which is identical to MrYs instructions

  4. rini94
    • 4 years ago
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    -4/5

  5. amistre64
    • 4 years ago
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    3-4-5 WAS a shortcut , cool lol

  6. MrYantho
    • 4 years ago
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    Then, from the triangle example (and amistre) you can use pythagorean theorem to find the unknown side (which is also the y-coord) \[y^2=1^2+(\frac{-3}{4})^2\] Solving this gives you 4/5, but you have to remember that since it is in Q3, it has to be negative.

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