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Ellipses - Example 1: Sketching 4x^2 + 9y^2 = 36

4x^2 + 9y^2 = 36 is the equation of an ellipse centred at the origin (0,0). Before we can sketch the ellipse, we need to find the vertices (i.e. the x and y intercepts) by transforming the equation to the standard form, which is:

x^2/a^2 + y^2/b^2

where...

a is the semi-major axis
b is the semi-minor axis

So, dividing the equation by 36, we get:

x^2/9 + y^2/4 = 1

Or...

x^2/3^2 + y/2^2 = 1

Thus a = 3 and b = 2, and hence the vertices are:

A = (3,0)
A' = (-3,0)
B = (0,2)
B' = (0,-2)

To fully define the ellipse, we should also find the focal points and the directrices. Thus we to find the eccentricity. We can do this through the relationship:

b^2 = a^2 - (ae)^2

The focal points (foci) are given by:

F = (ae,0)
F' = (-ae,0)

And the equations are of the directrices are:

x = a/e
x = -a/e

Suggested video:
- "Conic Sections: The Ellipse - Part 1" https://youtu.be/j3abHkwAFvY
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Видео Ellipses - Example 1: Sketching 4x^2 + 9y^2 = 36 канала MasterWuMathematics
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14 декабря 2015 г. 16:38:09
00:08:31
Яндекс.Метрика