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Question -

Find the equation of the circle which passes through the points (3, 7), (5, 5) and has its centre on line x тАУ 4y = 1.



Answer -

Given:

The points (3, 7), (5,5)

The line x тАУ 4y = 1тАж.(1)

By using the standardform of the equation of the circle:

x2┬а+ y2┬а+2ax + 2by + c = 0 тАж.. (2)

Let us substitute thecentre (-a, -b) in equation (1) we get,

(- a) тАУ 4(- b) = 1

-a + 4b = 1

a тАУ 4b + 1 = 0тАжтАж (3)

Substitute the points(3, 7) in equation (2), we get

32┬а+ 72┬а+2a(3) + 2b(7) + c = 0

9 + 49 + 6a + 14b + c= 0

6a + 14b + c + 58 =0тАж.. (4)

Substitute the points(5, 5) in equation (2), we get

52┬а+ 52┬а+2a(5) + 2b(5) + c = 0

25 + 25 + 10a + 10b +c = 0

10a + 10b + c + 50 =0тАж.. (5)

By simplifyingequations (3), (4) and (5) we get,

a = 3, b = 1, c = тАУ 90

Now, by substitutingthe values of a, b, c in equation (2), we get

x2┬а+ y2┬а+2(3)x + 2(1)y тАУ 90 = 0

x2┬а+ y2┬а+6x + 2y тАУ 90 = 0

тИ┤┬аThe equation ofthe circle is x2┬а+ y2┬а+ 6x + 2y тАУ 90 = 0.

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