Animated Solution for Mathematics - Circles: Choose the correct statement about two circles whose equations are given below:
x2+y2−10x−10y+41=0 and x2+y2−22x−10y+137=0
Select Answer:
Visualized Solution
Problem Statement
Circle C1:x2+y2−10x−10y+41=0
Circle C2:x2+y2−22x−10y+137=0
Goal: Find the number of meeting points between C1 and C2.
General Equation of a Circle
General Form: x2+y2+2gx+2fy+c=0
The center of the circle is at (−g,−f).
Center of C1
Compare C1 with the general form:
2g=−10⟹g=−5
2f=−10⟹f=−5
Center A=(5,5)
Radius Formula
Radius R=g2+f2−c
For C1, the constant term c=41.
Radius of C1
R1=(−5)2+(−5)2−41
R1=25+25−41
R1=9=3
Center of C2
For C2:x2+y2−22x−10y+137=0
2g=−22⟹g=−11
2f=−10⟹f=−5
Center B=(11,5)
Radius of C2
Here, c=137
R2=(−11)2+(−5)2−137
R2=121+25−137
R2=9=3
Distance Between Centers
To find how circles interact, we find the distance between centers A(5,5) and B(11,5).
Distance Formula: d=(x2−x1)2+(y2−y1)2
Calculating AB
AB=(11−5)2+(5−5)2
AB=62+02
AB=6
Condition for Touching Circles
Sum of radii: R1+R2=3+3=6
Distance between centers: AB=6
Observation: AB=R1+R2
Final Conclusion
Since AB=R1+R2, the circles touch each other externally.
Therefore, they have exactly one meeting point.
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The Sigma Insight: Standard and General Equation of a Circle
Solution Diagram
Analyzing the Setup
To understand the interaction between the two circles, we must first identify their fundamental properties: their centers and radii. The general equation of a circle is given by:
x2+y2+2gx+2fy+c=0
For a circle in this form, the center is (−g,−f) and the radius is calculated as R=g2+f2−c.
Decoding the Blueprints
For the first circle, C1, given by x2+y2−10x−10y+41=0, we identify g=−5, f=−5, and c=41.
The center A is (5,5). The radius R1 is:
R1=(−5)2+(−5)2−41=25+25−41=9=3
For the second circle, C2, given by x2+y2−22x−10y+137=0, we identify g=−11, f=−5, and c=137.
The center B is (11,5). The radius R2 is:
R2=(−11)2+(−5)2−137=121+25−137=9=3
The Geometric Bridge
Now that we have the centers A(5,5) and B(11,5), we calculate the distance d between them. Since the y-coordinates are identical, the distance is simply the difference in the x-coordinates:
d=(11−5)2+(5−5)2=62+02=6
The Moment of Truth
We compare the distance between the centers to the sum of the radii. We have R1=3 and R2=3, so:
R1+R2=3+3=6
Since the distance between the centers d is exactly equal to the sum of the radii (d=R1+R2), the circles are in a state of perfect external tangency.
They touch at exactly one point. The circles do not overlap, nor are they separated by any distance.