Equations of geometric shapes

Equation of a line
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Equation of a line (slope-intercept)
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Equation of a line (point-slope)
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Equation of a line from two points
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Equation of a circle whose center is at (x0, y0)
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Equation of a circle whose center is at the origin
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Equation of a sphere whose center is at (x0, y0, z0)
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Equation of a sphere whose center is at the origin
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