Chapter 3: Problem 68
Exer. 67-68: For the given circle, find (a) the \(x\)-intercepts and (b) the \(y\)-intercepts. $$ x^{2}+y^{2}-10 x+4 y+13=0 $$
Short Answer
Expert verified
The \(x\)-intercepts are \(5 \pm 2\sqrt{3}\); there are no \(y\)-intercepts.
Step by step solution
01
Rewrite Circle Equation in Standard Form
Start with the circle equation \(x^{2}+y^{2}-10x+4y+13=0\). To find intercepts, we first complete the square for both \(x\) and \(y\) terms to rewrite it in standard form \((x-h)^2 + (y-k)^2 = r^2\).
02
Complete the Square for x
Focus on the \(x\) terms: \(x^2 - 10x\). Complete the square by adding and subtracting \(25\): \(x^2 - 10x + 25 - 25\). This becomes \((x-5)^2 - 25\).
03
Complete the Square for y
Focus on the \(y\) terms: \(y^2 + 4y\). Complete the square by adding and subtracting \(4\): \(y^2 + 4y + 4 - 4\). This becomes \((y+2)^2 - 4\).
04
Rewrite the Equation
Substitute the completed squares back into the equation: \((x-5)^2 - 25 + (y+2)^2 - 4 + 13 = 0\). Simplify to get: \((x-5)^2 + (y+2)^2 = 16\).
05
Find x-intercepts
For \(x\)-intercepts, set \(y = 0\) in the standard form. Substitute \(y = 0\) into \((x-5)^2 + (y+2)^2 = 16\) which gives \((x-5)^2 + 4 = 16\). Simplify to \((x-5)^2 = 12\). Solve for \(x\) to find \(x = 5 \pm 2\sqrt{3}\).
06
Find y-intercepts
For \(y\)-intercepts, set \(x = 0\) in the standard form. Substitute \(x = 0\) into \((x-5)^2 + (y+2)^2 = 16\) which gives \(25 + (y+2)^2 = 16\). Simplify to \((y+2)^2 = -9\). Since this cannot yield real solutions, there are no \(y\)-intercepts.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
x-intercepts
X-intercepts are the points where the graph of an equation crosses the x-axis. To find them for a circle, set the y-coordinate to zero because the points lie directly on the x-axis. This reduces the circle equation to a simpler form that only has the variable x.
In this example, the circle equation \[(x-5)^2 + (y+2)^2 = 16\] is used. By setting y = 0, the equation becomes: \[(x-5)^2 + 4 = 16\].
Simplifying this gives \[(x-5)^2 = 12\]. Taking the square root of both sides, we find two potential x-intercepts: \(x = 5 + 2\sqrt{3}\) and \(x = 5 - 2\sqrt{3}\).
Thus, the x-intercepts are the points - \((5 + 2\sqrt{3}, 0)\)
- \((5 - 2\sqrt{3}, 0)\).
Understanding x-intercepts involves setting y = 0 and solving for x, revealing where the circle intersects the x-axis.
In this example, the circle equation \[(x-5)^2 + (y+2)^2 = 16\] is used. By setting y = 0, the equation becomes: \[(x-5)^2 + 4 = 16\].
Simplifying this gives \[(x-5)^2 = 12\]. Taking the square root of both sides, we find two potential x-intercepts: \(x = 5 + 2\sqrt{3}\) and \(x = 5 - 2\sqrt{3}\).
Thus, the x-intercepts are the points - \((5 + 2\sqrt{3}, 0)\)
- \((5 - 2\sqrt{3}, 0)\).
Understanding x-intercepts involves setting y = 0 and solving for x, revealing where the circle intersects the x-axis.
y-intercepts
Y-intercepts occur where the graph crosses the y-axis, meaning the x-coordinate is zero at these points. For a circle's equation, setting x to zero will simplify the equation and help determine the y-intercepts.
In the provided circle equation \[(x-5)^2 + (y+2)^2 = 16\], setting x = 0 yields \[25 + (y+2)^2 = 16\]. Simplifying this leads to \[(y+2)^2 = -9\].
Since the square of a number can't be negative and thus cannot equal -9, there are no real y-intercepts. This means that the circle doesn't cross the y-axis.
Y-intercepts are determined by setting x = 0 and examining the resulting equation. Here, the absence of real solutions indicates no points of intersection on the y-axis. This can sometimes happen with circles, especially when they sit to one side of the y-axis.
In the provided circle equation \[(x-5)^2 + (y+2)^2 = 16\], setting x = 0 yields \[25 + (y+2)^2 = 16\]. Simplifying this leads to \[(y+2)^2 = -9\].
Since the square of a number can't be negative and thus cannot equal -9, there are no real y-intercepts. This means that the circle doesn't cross the y-axis.
Y-intercepts are determined by setting x = 0 and examining the resulting equation. Here, the absence of real solutions indicates no points of intersection on the y-axis. This can sometimes happen with circles, especially when they sit to one side of the y-axis.
completing the square
Completing the square is a mathematical technique used to convert quadratic expressions or equations into a perfect square form. This process makes it easier to work with the equation, especially for graphing or solving purposes, such as finding the center and radius of a circle.
To complete the square for the equation \(x^2 - 10x\), focus solely on the x terms. Add and subtract \(25\) (which is \((10/2)^2\)), turning the expression into \((x - 5)^2 - 25\).
For the y terms \(y^2 + 4y\), adding and subtracting \(4\) (since \((4/2)^2\)), results in \((y + 2)^2 - 4\).
Substitute these completed squares back into the original equation to transform it to the standard form: \[(x-5)^2 + (y+2)^2 = 16\].
This crucial step is often used to bring a circle's equation from its general form to the standard form, simplifying the identification of the center point and radius.
To complete the square for the equation \(x^2 - 10x\), focus solely on the x terms. Add and subtract \(25\) (which is \((10/2)^2\)), turning the expression into \((x - 5)^2 - 25\).
For the y terms \(y^2 + 4y\), adding and subtracting \(4\) (since \((4/2)^2\)), results in \((y + 2)^2 - 4\).
Substitute these completed squares back into the original equation to transform it to the standard form: \[(x-5)^2 + (y+2)^2 = 16\].
This crucial step is often used to bring a circle's equation from its general form to the standard form, simplifying the identification of the center point and radius.
standard form of a circle equation
The standard form of a circle equation is a streamlined version that makes it easy to identify the circle's center and radius. The standard format is \((x-h)^2 + (y-k)^2 = r^2\), where \((h, k)\) represents the center of the circle, and \(r\) is the radius.
In this problem, after completing the square, we converted the given circle equation into standard form: \[(x-5)^2 + (y+2)^2 = 16\].
From this, it's clear that the center of the circle is at \((5, -2)\), and the radius is \(\sqrt{16} = 4\).
Using the standard form improves comprehension and allows for quick determination of the circle's geometric properties without additional calculation. Understanding this form is vital for not just circle-related calculations but also graphing them effectively.
In this problem, after completing the square, we converted the given circle equation into standard form: \[(x-5)^2 + (y+2)^2 = 16\].
From this, it's clear that the center of the circle is at \((5, -2)\), and the radius is \(\sqrt{16} = 4\).
Using the standard form improves comprehension and allows for quick determination of the circle's geometric properties without additional calculation. Understanding this form is vital for not just circle-related calculations but also graphing them effectively.