Ellipse formulae will help us to solve different types of problems on ellipse in coordinate geometry.
1. \(\frac{x^{2}}{a^{2}}\) + \(\frac{y^{2}}{b^{2}}\) = 1, (a > b)
(i) The coordinates of the centre are (0, 0).
(ii) The coordinates of the vertices are (± a, 0) i.e., (a, 0) and (a, 0).
(iii) The coordinates of the foci are (± ae, 0) i.e., ( ae, 0) and (ae, 0)
(iv) The length of major axis = 2a and the length of minor axis = 2b.
(v) The major axis is along x axis and the equations of major axes is y = 0.
(vi) The minor axis is along y axis and the equations of minor axes is x = 0.
(vii) The equations of the directrices are: x = ± \(\frac{a}{e}\) i.e., x =  \(\frac{a}{e}\) and x = \(\frac{a}{e}\).
(viii) The eccentricity of the ellipse is b\(^{2}\) = a\(^{2}\)(1  e\(^{2}\)) or, e = \(\sqrt{1  \frac{b^{2}}{a^{2}}}\).
(ix) The length of the latus rectum 2 ∙ \(\frac{b^{2}}{a}\) = 2a(1  e\(^{2}\)).
(x) The distance between the two foci = 2ae.
(xi) The distance between two directrices = 2 ∙ \(\frac{a}{e}\).
(xii) Focal distances of a point (x, y) are a ± ex
(xiii) The coordinates of the four ends of latera recta are (ae, \(\frac{b^{2}}{a}\)), (ae, \(\frac{b^{2}}{a}\)), ( ae, \(\frac{b^{2}}{a}\)) and ( ae, \(\frac{b^{2}}{a}\)).
(xiv) The equations of latera recta are x = ± ae i.e., x = ae and x = ae.
2. \(\frac{x^{2}}{b^{2}}\) + \(\frac{y^{2}}{a^{2}}\) = 1, (a > b)
(i) The coordinates of the centre are (0, 0).
(ii) The coordinates of the vertices are (0, ± a) i.e., (0, a) and (0, a).
(iii) The coordinates of the foci are (0, ± ae) i.e., (0,  ae) and (0, ae)
(iv) The length of major axis = 2a and the length of minor axis = 2b.
(v) The major axis is along Yaxis and the equations of major axes is x = 0.
(vi) The minor axis is along Xaxis and the equations of minor axes is y = 0.
(vii) The equations of the directrices are: y = ± \(\frac{a}{e}\) i.e., y =  \(\frac{a}{e}\) and y = \(\frac{a}{e}\).
(viii) The eccentricity of the ellipse is b2 = a\(^{2}\)(1  e\(^{2}\)) or, e = \(\sqrt{1  \frac{b^{2}}{a^{2}}}\)
(ix) The length of the latus rectum 2 ∙ \(\frac{b^{2}}{a}\) = 2a (1  e\(^{2}\)).
(x) The distance between the two foci = 2ae.
(xi) The distance between two directrices = 2 ∙ \(\frac{a}{e}\).
(xii) Focal distances of a point (x, y) are a ± ey
(xiii) The coordinates of the four ends of latera recta are (\(\frac{b^{2}}{a}\), ae), (\(\frac{b^{2}}{a}\), ae), (\(\frac{b^{2}}{a}\), ae) and (\(\frac{b^{2}}{a}\), ae).
(xiv) The equations of latera recta are y = ± ae i.e., y = ae and y = ae.
`3. \(\frac{(x  α)^{2}}{a^{2}}\) + \(\frac{(y  β)^{2}}{b^{2}}\) = 1, (a > b)
(i) The coordinates of the centre are (α, β).
(ii) The coordinates of the vertices are (α ± a, β) i.e., (α  a, β) and (α + a, β).
(iii) The coordinates of the foci are (α ± ae, β) i.e., (α  ae, β) and (α + ae, β)
(iv) The length of major axis = 2a and the length of minor axis = 2b.
(v) The major axis is along parallel to x axis and the equations of major axes is y = β.
(vi) The minor axis is along parallel to y axis and the equations of minor axes is x = α.
(vii) The equations of the directrices are: x = α ± \(\frac{a}{e}\) i.e., x = α  \(\frac{a}{e}\) and x = α + \(\frac{a}{e}\).
(viii) The eccentricity of the ellipse is b\(^{2}\) = a\(^{2}\)(1  e\(^{2}\)) or, e =\(\sqrt{1  \frac{b^{2}}{a^{2}}}\)
(ix) The length of the latus rectum 2 ∙ \(\frac{b^{2}}{a}\) = 2a (1  e\(^{2}\)).
(x) The distance between the two foci = 2ae.
(xi) The distance between two directrices = 2 ∙ \(\frac{a}{e}\).
4. \(\frac{(x  α)^{2}}{b^{2}}\) + \(\frac{(y  β)^{2}}{a^{2}}\) = 1, (a > b)
(i) The coordinates of the centre are (α, β).
(ii) The coordinates of the vertices are (α, β ± a) i.e., (α, β  a) and (α, β + a).
(iii) The coordinates of the foci are (α, β ± ae) i.e., (α, β  ae) and (α, β + ae).
(iv) The length of major axis = 2a and the length of minor axis = 2b.
(v) The major axis is along parallel to Yaxis and the equations of major axes is x = α.
(vi) The minor axis is along parallel to Xaxis and the equations of minor axes is y = β.
(vii) The equations of the directrices are: y = β ± \(\frac{a}{e}\) i.e., y = β  \(\frac{a}{e}\) and y = β + \(\frac{a}{e}\).
(viii) The eccentricity of the ellipse is b\(^{2}\) = a\(^{2}\)(1  e\(^{2}\)) or, e = \(\sqrt{1  \frac{b^{2}}{a^{2}}}\)
(ix) The length of the latus rectum 2 ∙ \(\frac{b^{2}}{a}\) = 2a (1  e\(^{2}\)).
(x) The distance between the two foci = 2ae.
(xi) The distance between two directrices = 2 ∙ \(\frac{a}{e}\).
5. The point P (x\(_{1}\), y\(_{1}\)) lies outside, on or inside the ellipse \(\frac{x^{2}}{a^{2}}\) + \(\frac{y^{2}}{b^{2}}\) = 1 according as \(\frac{x_{1}^{2}}{a^{2}}\) + \(\frac{y_{1}^{2}}{b^{2}}\) – 1 > 0, = or < 0.
6. If \(\frac{x^{2}}{a^{2}}\) + \(\frac{y^{2}}{b^{2}}\) = 1 is an ellipse, then its auxiliary circle is x\(^{2}\) + y\(^{2}\) = a\(^{2}\).
7. The equations x = a cos ф, y = b sin ф taken together are called the parametric equations of the ellipse \(\frac{x^{2}}{a^{2}}\) + \(\frac{y^{2}}{b^{2}}\) = 1
8. The coordinates of the point having eccentric angle ф can be written as (a cos ф, b sin ф). Here (a cos ф, b sin ф) are known as the parametric coordinates of the point P.
`2nd Grade Math Practice
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