The general equation of a circle with center (h, k) and radius r is?
A
(x - h)² + (y - k)² = r²
C
x² + y² + 2gx + 2fy + c = 0
D
(x + h)² + (y + k)² = r²
Analysis & Theory
The standard form is (x - h)² + (y - k)² = r², where (h, k) is the center and r is the radius.
The equation of a circle with center at origin (0,0) and radius r is?
B
(x - 0)² + (y - 0)² = r²
Analysis & Theory
All given forms represent the same circle centered at origin with radius r.
The equation of a circle with center (3, -2) and radius 5 is?
A
(x - 3)² + (y + 2)² = 25
B
(x + 3)² + (y - 2)² = 25
C
(x - 2)² + (y - 3)² = 25
D
(x + 2)² + (y + 3)² = 25
Analysis & Theory
Equation: (x - h)² + (y - k)² = r² ⇒ (x - 3)² + (y - (-2))² = 25.
If the circle has equation (x - 1)² + (y + 4)² = 16, then the radius is?
Analysis & Theory
Here r² = 16, so radius r = 4.
In the circle (x - 5)² + (y + 7)² = 36, the center is?
Analysis & Theory
Equation (x - h)² + (y - k)² = r² ⇒ center is (5, -7).
The equation x² + y² - 6x + 8y + 9 = 0 represents a circle with center?
Analysis & Theory
Complete the square: x² - 6x + y² + 8y + 9 = 0 ⇒ (x - 3)² + (y + 4)² = 16. Center = (3, -4).
The radius of the circle x² + y² - 4x - 6y - 12 = 0 is?
Analysis & Theory
Completing square: (x - 2)² + (y - 3)² = 25 ⇒ r = √25 = 5. Wait correction: (x² - 4x) + (y² - 6y) = 12 ⇒ (x - 2)² - 4 + (y - 3)² - 9 = 12 ⇒ (x - 2)² + (y - 3)² = 25 ⇒ r = 5.
Which of the following is the correct radius of circle (x + 1)² + (y - 2)² = 49?
Analysis & Theory
Since r² = 49, radius = √49 = 7. Options 1 and 3 both mean 7.
Equation (x - h)² + (y - k)² = 0 represents?
A
A point circle at (h, k)
Analysis & Theory
Radius = 0 ⇒ the circle reduces to a single point (h, k).
If a circle has center (2, -3) and passes through (5, 1), its equation is?
A
(x - 2)² + (y + 3)² = 25
B
(x + 2)² + (y - 3)² = 25
C
(x - 5)² + (y - 1)² = 25
D
(x - 2)² + (y + 3)² = 16
Analysis & Theory
Radius = distance between (2, -3) and (5, 1) = √[(5-2)² + (1+3)²] = √(9+16) = 5 ⇒ equation: (x - 2)² + (y + 3)² = 25.