THE EQUATION OF THE CIRCLE
HANDOUT FOR GRADE 10 ENRICHED
By Alex Pintilie
Together:
1) Write the equation of the circle with centre (0,0) and passing through (3, - 4).
2) Write the equation of the circle with centre ( - 2, 3) and radius 5.
3) Write the equation of the circle with centre (1, -2) and passing through (4, - 6).
4) State the radius and the coordinates of the centre of the circle of equation:
a. x2 + y2 + 6x – 27 = 0
b. x2 + y2 + 10x – 8y + 16 = 0
5) Find the x- and the y- intercepts of the circle of equation: (x-5)2+(y+1)2=50. Draw the circle.
6) A circle with centre on the y-axis passes through A(-3, 0) and B(5,4). Write the equation of the circle. Draw the circle and indicate on the figure the points A and B.
7) For the circle given by x2+y2 = 34
a. show that the line segment from P(-5,3) to Q(3,5) is a chord of the circle;
b. find the midpoint M of the chord;
c. show that MO ┴ PQ.
Homework:
1) Write the equation of the circle with centre (0,0) and passing through (- 2 , - 5).
2) Write the equation of the circle with centre ( 4, 3) and radius 2.
3) Write the equation of the circle with centre (3, -2) and passing through (5, 1).
4) State the radius and the coordinates of the centre of the circle of equation:
a. x2 + y2 – 4y – 5 = 0
b. x2 + y2 – 4x + 2y – 4 = 0
5) Find the x- and the y- intercepts of the circle of equation: (x+4)2+(y-3)2=25. Draw the circle.
6) A circle with centre on the x-axis passes through A(6, 4) and B(-1,3). Write the equation of the circle. Draw the circle and indicate on the figure the points A and B.
7) Given the circle x2+y2+8x – 6y = 0,
a. show that the circle passes through O(0,0),
b. if O is one end of the diameter of the circle, find the other end P,
c. pick any other point Q on the circle and show that the angle OQP = 90o
8) (This is a tough one.) A circle with centre on the line x + 2y = 4 passes through the points A(6,9) and B(12, -9). Write the equation of the circle.
Answers: 1) x2+y2=29 2) (x-4)2+(y-3)2=4 3) (x-3)2+(y+2)2=13
4) a) r = 1, C(0,2) b) r=3, C(2,-1) 5) x= 0, x= -8; y = 0, y = 6
6) (x-3)2 + y2 = 25 7) b) P(-8,6) 8) (x-6)2 + (y+1)2 = 100
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