Chapter 19: Problem 106
Assertion: If the point \((2,4)\) is interior to the circle \(x^{2}\) \(+y^{2}-6
x-10 y+k=0\) and the circle does not cut the axes at any point, then \(25
Short Answer
Expert verified
The assertion and reason correctly imply that \(25 < k < 32\).
Step by step solution
01
Understand the Circle Equation
The given equation of the circle is \( x^2 + y^2 - 6x - 10y + k = 0 \). This can be rewritten in standard circle form \((x - h)^2 + (y - k)^2 = r^2\) after completing the square. Thus, compare this equation with \((x - 3)^2 + (y - 5)^2 = r^2\). Here, the circle has center \((3, 5)\).
02
Determine the Criterion for Interior Point
According to the Reason, if a point \((x_1, y_1)\), lies inside the circle given by \(x^2 + y^2 + 2gx + 2fy + c = 0\), then \(x_1^2 + y_1^2 + 2gx_1 + 2fy_1 + c < 0\). For the circle \( x^2 + y^2 - 6x - 10y + k = 0 \), we identify \(2g = -6\), \(2f = -10\), so \(g = -3\) and \(f = -5\).
03
Substitute Point into the Inequality
Substitute \((x_1, y_1) = (2, 4)\) into the inequality: \[2^2 + 4^2 - 6 \times 2 - 10 \times 4 + k < 0\]. Compute: \[4 + 16 - 12 - 40 + k < 0\]. Simplify to get: \[-32 + k < 0\].
04
Solve for k using Interior Point Criterion
From \(-32 + k < 0\), we have \(k < 32\). Thus, for the point to be interior, \(k < 32\).
05
Use the Condition Circle Does Not Cut Axes
The circle does not cut the x-axis and y-axis. The circle equation implies if it does not cut the axes, then \(c > 0\) is required, where \(c = k\). Thus, \(k > 25\) because the radius is less than 0 when equal to 25. Evaluate where \((3, 0)\text{ to not cut x-axis and }(0, 5)\text{ to not cut y-axis} \), these give lower bounds with \(25 < k\).
06
Conclude the Inequality for k
Combine both conditions: \(25 < k < 32\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Circle Equation
In coordinate geometry, the equation of a circle plays a crucial role in understanding the properties and positions of circles on the Cartesian plane. The general form of a circle's equation is given by:
- \(x^2 + y^2 - 6x - 10y + k = 0\)
- \((x - h)^2 + (y - k)^2 = r^2\),
- is found at \((3, 5)\).
- This occurs through rearranging terms and observing the coefficients of \(x\) and \(y\).
- The center is \((h,k) = (3, 5)\),
- and its radius \(r\)
Interior Point
Determining whether a point lies inside a circle involves utilizing the circle's equation. A given point
- such as \((2, 4)\)
- \(x_1^2 + y_1^2 + 2gx_1 + 2fy_1 + c < 0\)
- is inside the circle.
- \(x_1 = 2\) and
- \(y_1 = 4\),
- \(x^2 + y^2 - 6x - 10y + k\),
- \(-32 + k < 0\).
- if the point is internal or not based on the value of \(k\).
Inequality for k
The variable \(k\) in the circle equation impacts the positioning and size of the circle on the plane. To determine acceptable values for \(k\), ensure both the point
- \((2, 4)\)
- to be inside, \(-32 + k < 0\), and
- therefore, \(k < 32\).
- note that \(c\), or equivalently \(k\) in the original equation, must be positive.
- The radius squared must be larger than zero due to \((3\),
- 0) and \((0\), involving the formula
- 5).
- This gives a lower bound such that \(k > 25\).
- \(25 < k < 32\)