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Question: Answered & Verified by Expert
A circle has its centre in the first quadrant and passes through 2,3. If this circle makes intercepts of length 3 and 4 respectively on x=2 and y=3, its equation is
MathematicsCircleAP EAMCETAP EAMCET 2022 (04 Jul Shift 2)
Options:
  • A x2+y2+3x-5y+8=0
  • B x2+y2-4x-6y+13=0
  • C x2+y2-6x-8y+23=0
  • D x2+y2-8x-9y+30=0
Solution:
1646 Upvotes Verified Answer
The correct answer is: x2+y2-8x-9y+30=0

Consider a circle with centre be a,b.

So the equation of circle will be,

x2+y2-2ax-2by+c=0      1

In the question it is given that the circle passes through 2,3.

Therefore, substituting x=2 and y=3 respectively in the equation 1 we get,

22+32-2a×2-2b×3+c=0

13-4a-6b+c=0

  c=4a+6b-13

So now putting the value of c in the equation 1 we get,

x2+y2-2ax-2by+4a+6b-13=0       2

Now we will find intercept on line x=2, y=3 respectivley.

By substituting x=2 in the equation 1 we get,

4+y2-4a-2by+4a+6b-13=0       3

In the equation 3 let y1,y2 be the roots.

So, from equation 3 sum of the roots will be,

y1+y2=2b      4

Product of the roots will be,

y1y2=6b-9       5

Now as we know that length of intercept is y1-y2. So we will use the identity, a-b=a+b2-4ab

y1-y2=y1+y22-4y1y2

32=y1+y22-4y1y2

Substituting the values of equation 4 and 5, we get

9=2b2-46b-9

4b2-24b+27=0

4b2-6b-18b+27=0

2b2b-3-92b-3=0

2b-92b-3=0

b=92,b=32

Hence the values of b is 92 or 32

By substituting the value of y=3 in the euqation 2 we get,

x2+9-2ax-6b+4a+6b-13=0

x2-2ax+4a-4=0      6

In equation 6 let x1,x2 be the roots,

Sum of the roots will be,

x1+x2=2a      7

Product of the roots will be

x1x2=4a-4      8

Again using same identity we get,

x1-x2=x1+x22-4x1x2

4=x1+x22-4x1x2

4=2a2-44a-4

4=a2-4a-4

a2-4a=0

aa-4=0

Here the value of a is 0 or 4.

So now there are 4 such sets of equation can be made by the sets of vales of a,b which are

0,32,0,92,4,32 and 4,92.

For 0,32 we will substitute in equation 3, we get

x2+y2-2ax-2by+4a+6b-13=0

x2+y2-2x0-2y×32+4(0)+6×32-13=0

 x2+y2-3y+-4=0

For 0,92 we will substitue in equation 3, we get

x2+y2-2ax-2by+4a+6b-13=0

x2+y2-2x0-2y×92+40+6×92-13=0

 x2+y2-9y+14=0

For 4,32 we will substitue in euqation 3, we get

x2+y2-2ax-2by+4a+6b-13=0

x2+y2-2x4-2y×32+44+6×32-13=0

  x2+y2-8x-3y+12=0

For 4,92 we will substitute in equation 3, we get

x2+y2-2ax-2by+4a+6b-13=0

x2+y2-2x4-2y×92+44+6×92-13=0

  x2+y2-8x-9y+30=0

So only x2+y2-8x-9y+30=0 is matching with the given option.

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