What is the standard deviation of a dataset: {6, 9, 3, 12, 7, 1, 18, 13, 4}?
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Find the equation of the ellipse with a major axis length 10 units, minor axis length 6 units, center at (2, -3), and major axis parallel to the y-axis.
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What is the value of the sine of an angle if its cosine is -0.5?