Chapter 1: Problem 24
Do the graphs intersect in the given viewing rectangle? If they do, how many points of intersection are there? $$y=\sqrt{49-x^{2}}, y=\frac{1}{5}(41-3 x) ; \quad[-8,8] \text { by }[-1,8]$$
Short Answer
Expert verified
There are two intersection points within the viewing rectangle.
Step by step solution
01
Understand the Functions
The first function, \( y = \sqrt{49 - x^2} \), is the equation of a circle centered at the origin with a radius of 7, but only the top half of it (since it involves a square root). The second function, \( y = \frac{1}{5}(41 - 3x) \), is a linear equation representing a line with a slope of \(-\frac{3}{5}\) and a y-intercept of \(\frac{41}{5}\).
02
Set Equations Equal to Find Intersections
To find intersection points, we solve for \( x \) where \( \sqrt{49 - x^2} = \frac{1}{5}(41 - 3x) \). First, simplify: \( 5\sqrt{49 - x^2} = 41 - 3x \).
03
Square Both Sides
Square both sides to eliminate the square root: \[ 25(49 - x^2) = (41 - 3x)^2 \]. This leads to \( 1225 - 25x^2 = 1681 - 246x + 9x^2 \).
04
Simplify and Rearrange the Equation
Rearrange and simplify the equation: \(-34x^2 + 246x - 456 = 0\), then divide everything by 2 to simplify: \(-17x^2 + 123x - 228 = 0\).
05
Solve the Quadratic Equation
Use the quadratic formula \( x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} \), where \( a = -17 \), \( b = 123 \), and \( c = -228 \). Calculate \( \Delta = b^2 - 4ac = 123^2 - 4(-17)(-228) \). Evaluate \( \Delta \) to find the roots of the equation.
06
Calculate the Discriminant
Calculate \( \Delta = 15129 - 4 \times 17 \times 228 \). Compute this to find \( \Delta = 289 \).
07
Find the Roots
Substitute \( \Delta = 289 \) into the quadratic formula: \( x = \frac{-123 \pm 17}{-34} \). This gives two possible \( x \) values. Calculate these values.
08
Determine Intersection Points Within Range
Check if the \( x \) values calculated fall within the interval \([-8, 8]\). If they do, compute corresponding \( y \) values using either equation.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Circle Equation
The equation of a circle is usually written in the form: \[x^2 + y^2 = r^2\]Here, \(r\) represents the radius of the circle. A standard circle centered on the origin \( (0,0) \) is derived from this equation. In the exercise provided, the circle equation is given as \( y = \sqrt{49 - x^2} \). This represents only the upper half of a circle. Why only the upper half? Because by taking the square root, we consider only the positive values of \(y\).
- The center is at the origin \((0, 0)\).
- The radius is 7, since \( \sqrt{49} = 7 \).
Linear Equation
Linear equations represent straight lines. These can be given in several forms: slope-intercept, point-slope, or standard form. For this problem, we're dealing with a slope-intercept form given as:\[y = \frac{1}{5}(41 - 3x)\]This represents a line with:
- A slope of \(-\frac{3}{5}\), indicating how steep the line climbs or descends.
- A y-intercept of \frac{41}{5}\, showing where the line crosses the y-axis.
Quadratic Formula
When equations become quadratic, the quadratic formula offers a way to find their roots or solutions. It's expressed as:\[x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}\]To solve our equation for intersection, we must transform the expression we derived by setting the circle equation equal to the linear equation, resulting in a quadratic form:
\[-17x^2 + 123x - 228 = 0\]Here:
\[-17x^2 + 123x - 228 = 0\]Here:
- \(a = -17\)
- \(b = 123\)
- \(c = -228\)
Discriminant Calculation
The discriminant, noted as \(\Delta\), plays a big role in determining the nature of the solutions of a quadratic equation. It is found using the formula:\[\Delta = b^2 - 4ac\]In our problem, this calculation shows whether the quadratic equation has real and distinct, real and repeated, or imaginary roots:
- If \(\Delta > 0\), two distinct real roots exist.
- If \(\Delta = 0\), exactly one real root is present (a double root).
- If \(\Delta < 0\), no real roots, implying no intersection within real numbers.