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The point A has co-ordinates (8, 6) and O is the origin - Leaving Cert Mathematics - Question Question 1 - 2013

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The point A has co-ordinates (8, 6) and O is the origin. The diagram shows two circles c₁ and c₂. c₁ has centre (0, 0) and radius |OA|. c₂ has a diameter of [OA]. ... show full transcript

Worked Solution & Example Answer:The point A has co-ordinates (8, 6) and O is the origin - Leaving Cert Mathematics - Question Question 1 - 2013

Step 1

Find the equation of c₁.

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Answer

To find the equation of the circle c₁, we start by determining the radius |OA|:

OA=extsqrt((80)2+(60)2)|OA| = ext{sqrt}((8-0)^2 + (6-0)^2) =extsqrt(64+36) = ext{sqrt}(64 + 36) =extsqrt(100) = ext{sqrt}(100) =10. = 10.
The equation of a circle is given by:

(xh)2+(yk)2=r2(x - h)^2 + (y - k)^2 = r^2
where (h, k) is the center and r is the radius. Since c₁ has its center at (0, 0) and radius 10, we get:

x2+y2=102x^2 + y^2 = 10^2 =100. = 100.
Thus, the equation of c₁ is:

Answer:
x2+y2=100x^2 + y^2 = 100

Step 2

Find the equation of c₂.

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Answer

The center of circle c₂ can be found by averaging the coordinates of points O (0, 0) and A (8, 6):

extCenter=(8+02,6+02)=(4,3). ext{Center} = \left( \frac{8 + 0}{2}, \frac{6 + 0}{2} \right) = (4, 3).

Next, the diameter of c₂ is equal to the distance |OA|, which we found earlier to be 10. Therefore, the radius r of c₂ is:

r=102=5. r = \frac{10}{2} = 5.
Using the equation of a circle:

(xh)2+(yk)2=r2(x - h)^2 + (y - k)^2 = r^2
we substitute (h, k) with (4, 3) and r with 5:

(x4)2+(y3)2=52(x - 4)^2 + (y - 3)^2 = 5^2 =25.= 25.
Thus, the equation of c₂ is:

Answer:
(x4)2+(y3)2=25(x - 4)^2 + (y - 3)^2 = 25

Step 3

The circle c₂ cuts the x-axis at the point P. Find the co-ordinates of P.

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Answer

To find where the circle c₂ intersects the x-axis, we set y = 0 in the equation of c₂:

(x4)2+(03)2=25(x - 4)^2 + (0 - 3)^2 = 25 (x4)2+9=25(x - 4)^2 + 9 = 25 (x4)2=259(x - 4)^2 = 25 - 9 (x4)2=16(x - 4)^2 = 16 Taking the square root of both sides gives:

x4=4extorx4=4x - 4 = 4 ext{ or } x - 4 = -4 Thus,

x=8extorx=0. x = 8 ext{ or } x = 0.
The corresponding coordinates at these points are:

  1. For x = 8, P(8, 0).
  2. For x = 0, P(0, 0).

The co-ordinates of P are:

Answer:
P(8, 0) and P(0, 0)

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