Chapter 2: Problem 102
Suppose \(b>a>0\). Find a formula in terms of \(y\) for the distance from a typical point \((x, y)\) on the ellipse \(\frac{x^{2}}{a^{2}}+\frac{y^{2}}{b^{2}}=1\) to the point \(\left(0, \sqrt{b^{2}-a^{2}}\right)\).
Short Answer
Expert verified
The short version of the answer is:
\[d = \sqrt{a^2 - \frac{a^2 y^2}{b^2} + y^2 - 2y\sqrt{b^2 - a^2} + b^2 - a^2}\]
Step by step solution
01
Recall the distance formula
The distance formula between two points \((x_1, y_1)\) and \((x_2, y_2)\) is given by:
\[
d = \sqrt{(x_2 - x_1)^2 + (y_2 - y_1)^2}
\]
02
Plug in the points' coordinates
We have the points \((x, y)\) and \(\left(0, \sqrt{b^2 - a^2}\right)\). So, \((x_1, y_1) = (x, y)\) and \((x_2, y_2) = \left(0, \sqrt{b^2 - a^2}\right)\). We can now substitute the coordinates into the distance formula:
\[
d = \sqrt{(-x)^2 + (y - \sqrt{b^2 - a^2})^2}
\]
03
Simplify the expression
The distance can be simplified as follows:
\begin{align*}
d &= \sqrt{x^2 + (y - \sqrt{b^2 - a^2})^2} \\
d &= \sqrt{x^2 + y^2 - 2y\sqrt{b^2 - a^2} + b^2 - a^2}
\end{align*}
04
Substitute \(x^2\) with the ellipse equation
From the equation of the ellipse, we have \(x^2 = a^2\left(1 - \frac{y^2}{b^2}\right)\). Let's substitute this into our distance formula:
\begin{align*}
d &= \sqrt{a^2\left(1 - \frac{y^2}{b^2}\right) + y^2 - 2y\sqrt{b^2 - a^2} + b^2 - a^2}
\end{align*}
05
Simplify the expression further
Now we can simplify the expression to get the distance in terms of \(y\):
\begin{align*}
d &= \sqrt{a^2 - \frac{a^2 y^2}{b^2} + y^2 - 2y\sqrt{b^2 - a^2} + b^2 - a^2}
\end{align*}
Hence, the distance formula for a typical point \((x,y)\) on the ellipse to the point \(\left(0, \sqrt{b^2 - a^2}\right)\) is:
\[
d = \sqrt{a^2 - \frac{a^2 y^2}{b^2} + y^2 - 2y\sqrt{b^2 - a^2} + b^2 - a^2}
\]
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Distance Formula
The distance formula is a straightforward and crucial tool in geometry. It helps us find the distance between two points in a coordinate plane. This formula is rooted in the Pythagorean theorem, making it easy to understand. The formula itself is given by:
- The distance \(d\) between two points \((x_1, y_1)\) and \((x_2, y_2)\) can be calculated using \(d = \sqrt{(x_2 - x_1)^2 + (y_2 - y_1)^2}\).
- In essence, it measures the length of the hypotenuse of a right triangle formed by the x and y differences.
- Square the difference in the x-coordinates.
- Square the difference in the y-coordinates.
- Add these squares together.
- Take the square root of this sum.
Conic Sections
Conic sections are curves obtained by intersecting a plane with a double-napped cone. They are a foundational concept in coordinate geometry, having applications in various fields such as astronomy, physics, and engineering. The primary types of conic sections are:
- Circle: A special type of ellipse where the two foci coincide.
- Ellipse: A set of points where the sum of the distances from two distinct foci is constant.
- Parabola: A set of points equidistant from a point (focus) and a line (directrix).
- Hyperbola: A set of points where the absolute difference of the distances to two foci is constant.
- \(a\) and \(b\) are the distances from the center to the vertices along the x and y axes, respectively.
- The foci are along the major axis, and their separation can be calculated using \(\sqrt{b^2 - a^2}\).
Coordinate Geometry
Coordinate geometry, also known as analytic geometry, combines algebra and geometry to study geometric figures. It utilizes a coordinate plane to define locations and shapes. Here are some core aspects:
- Every point in the plane is defined by a pair of numbers \((x, y)\).
- This system simplifies the process of calculating lengths, angles, and areas.
- It allows expressing geometric problems algebraically.
- An ordered pair \((x, y)\) representing each point.
- Equations that describe geometric shapes or paths.