The equations for hyperbolas are very similar to those for ellipses,
only with a minus sign.
The standard rectangular formulas for hyperbolas are x2a2−y2b2=1andy2a2−x2b2=1.The
first has foci at (±c,0), where c2=a2+b2 (instead of
a2−b2 for an ellipse), and the second has foci at (0,±c). As
before, the ratio c/a is called the eccentricity, only now it is
bigger than 1.
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The hyperbola x2−y2=1 opens to the sides.
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The hyperbola y2−x2=1 opens up and down.
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Hyperbolas can also be described by a distance formula.
Amazing fact for hyperbolas: The hyperbola is the set of all points where
|L1−L2|=2a.
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(This Amazing Fact can be derived almost exactly the same way
that we derived the Amazing Fact for ellipses.)
A hyperbola consists of two pieces, one with L1−L2=2a and one
with L1−L2=−2a. The four ends approach the lines y=±bax (for the first kind of hyperbola) or y=±abx (for the second kind). These lines are called
asymptotes.
Example: The asymptotes of the hyperbola x2−y2=2 are
the diagonal lines y=±x. If you rotate this hyperbola
counter-clockwise by 45 degrees, you get the curve y=1x,
whose asymptotes are the x and y axes.
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