The equation of a circle with centre C is x2+y2−8x−2y−152=0x^{2}+y^{2}-8x-2y-152=0.

  1. (i)

    Find the coordinates of C and the radius of the circle.

    Find the coordinates of C and the radius of the circle.

  2. (ii)

    Show that the point P(9, 13) lies on the circle.

    Show that the point P(9, 13) lies on the circle.

  3. (iii)

    A line, l is parallel to the tangent to the circle at P. Q is a point on line l such that P is the midpoint of the line QC.

    1. (a)

      Find the equation of the line l.

    2. (b)

      Explain if the line l will intersect the circle.

Work through it with AI →

It won't just hand you the answer — it asks where you're stuck.How the checker works

Worked solution

9(i)

1. Group the $x$ and $y$ terms and move the constant to the right side

x2−8x+y2−2y=152x^{2} - 8x + y^{2} - 2y = 152

2. Complete the square for $x$ and $y$

(x−4)2−16+(y−1)2−1=152(x - 4)^{2} - 16 + (y - 1)^{2} - 1 = 152
(x−4)2+(y−1)2=152+16+1(x - 4)^{2} + (y - 1)^{2} = 152 + 16 + 1

3. Simplify to standard circle equation form

(x−4)2+(y−1)2=169(x - 4)^{2} + (y - 1)^{2} = 169

4. Extract the centre coordinates and radius

Centre C is (4,1)(4, 1).
Radius r=169=13r = \sqrt{169} = 13.

Answer

Coordinates of C: (4,1)(4, 1), Radius: 1313

9(ii)

1. Substitute the coordinates of P into the left-hand side of the circle's equation.

Substitute x=9x = 9 and y=13y = 13 into x2+y2−8x−2y−152x^{2}+y^{2}-8x-2y-152:
LHS=(9)2+(13)2−8(9)−2(13)−152\text{LHS} = (9)^{2} + (13)^{2} - 8(9) - 2(13) - 152

2. Evaluate the expression to show it equals 0.

LHS=81+169−72−26−152\text{LHS} = 81 + 169 - 72 - 26 - 152
LHS=250−250=0\text{LHS} = 250 - 250 = 0
Since LHS=RHS\text{LHS} = \text{RHS}, the point P(9,13)P(9, 13) lies on the circle.

Answer

Since the substitution yields 00, the point P(9,13)P(9, 13) lies on the circle.

9(iii)(a)

1. Find the coordinates of the centre C from part (i)

From the circle equation x2+y2−8x−2y−152=0x^{2}+y^{2}-8x-2y-152=0, completing the square gives:
(x−4)2−16+(y−1)2−1−152=0(x-4)^2 - 16 + (y-1)^2 - 1 - 152 = 0
(x−4)2+(y−1)2=169(x-4)^2 + (y-1)^2 = 169
Centre CC is (4,1)(4, 1).

2. Find the gradient of the line l

Gradient of CP=13−19−4=125CP = \frac{13 - 1}{9 - 4} = \frac{12}{5}
The tangent at PP is perpendicular to the radius CPCP, so its gradient is −512-\frac{5}{12}.
Since line ll is parallel to the tangent, the gradient of line ll is also −512-\frac{5}{12}.

3. Find the coordinates of Q

Let QQ be (x,y)(x, y). Since P(9,13)P(9, 13) is the midpoint of QCQC:
x+42=9  ⟹  x=14\frac{x + 4}{2} = 9 \implies x = 14
y+12=13  ⟹  y=25\frac{y + 1}{2} = 13 \implies y = 25
So, QQ is (14,25)(14, 25).

4. Find the equation of line l

Using the point Q(14,25)Q(14, 25) and gradient m=−512m = -\frac{5}{12}:
y−25=−512(x−14)y - 25 = -\frac{5}{12}(x - 14)
12y−300=−5x+7012y - 300 = -5x + 70
5x+12y=3705x + 12y = 370

Answer

5x+12y=3705x + 12y = 370

9(iii)(b)

1. Determine the perpendicular distance from the centre C to the line $l$

Since line ll is parallel to the tangent at P, it is perpendicular to the radius CP.
Because P is the midpoint of QC, the points C, P, and Q are collinear.
Thus, the line segment CQ is perpendicular to ll at Q, meaning the perpendicular distance from the centre C to line ll is the length CQ.

2. Compare the distance CQ with the radius of the circle to conclude

Since P is the midpoint of QC, CQ=2×CPCQ = 2 \times CP.
Since CP is the radius of the circle, CQCQ is twice the radius (CQ=26>13CQ = 26 > 13).
Because the perpendicular distance from the centre to line ll is strictly greater than the radius, the line ll lies entirely outside the circle and will not intersect it.

Answer

The line ll will not intersect the circle because its perpendicular distance from the centre is greater than the radius.

AI analysis — may contain mistakes.

Worked this one out on paper? Snap your steps and Gigle's AI math checker will circle the step where it went wrong.

More questions on this topic

  1. 1The curve CC has equation y=x2+x+3x−2y = \frac{x^2 + x + 3}{x - 2}. Without using a calculator, find the set of values that yy…
  2. 2Find the gradient function of the curve y=2x2−ln⁡x+cy = 2x^2 - \ln x + c. The curve touches the positive xx-axis at point TT. Fi…
  3. 3The radius of a circle increases at a rate of 3 cm s^{-1}. Find, in terms of π\pi, the rate of increase of the area whe…
  4. 4定积分∫01(2x−x2)dx\int_{0}^{1}(\sqrt{2x{-}x^{2}})dx等于()({ }) A. π4\dfrac{\pi}{4} B. π2\dfrac{\pi}{2} C. π−14\dfrac{\pi{-}1}{4}…
  5. 5已知两定点M(0,1)M(0,1),N(1,2)N(1,2),平面内一动点PP到MM的距离与PP到NN的距离之比为2 \sqrt {2},直线y=kx−1y=kx-1与点PP的轨迹交于AA,BB两点. (…