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The area of the region formed by line segments joining the points of intersection of the circle $x^2+y^2-10x-6y+9=0$ with the two axes in succession in a definite order (clockwise or anticlockwise) is

  1. $16$
  2. $9$
  3. $3$
  4. $12$
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$\mathbf B$?
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@`JEET

I guess the answer must be i.e 12.

The circle intersects the x-axis and y-axis at points (0,3), (1,0) and (9,0).

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Yes, right!!
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1 Answer

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The equation of the circle can be rewritten as : $\left ( x-5 \right )^{2}+(y-3)^{2}=25$

For finding the intersection with $x-axis$ and $y-axis$, put $x=0$  and $y=0$   in the above equation.

So we get intesection points as :  $\left ( 0,3 \right )(1,0)(9,0)$

Area of the triangle formed by the line segments joining these points can be found using Heron's formula

i.e.  $A=\sqrt{s(s-a)(s-b)(s-c)}$   where $s$  is the semi-perimeter of the triangle defined as  $s=\frac{a+b+c}{2}$   ($a,b,c$  being the sides of triangle)

For the triangle formed, $a,b,c$  can be found using Euclid's distance formula .

Then after calculating lengths of $a,b,c$,  they are  :  $a=8,b=\sqrt{90},c=\sqrt{10}$   (values can be taken in any order ).

$\therefore$    $s=\frac{8+\sqrt{90}+\sqrt{10}}{2}=2\sqrt{10}+4$

Now,   $A=\sqrt{(2\sqrt{10}+4)(2\sqrt{10}+4-8)(2\sqrt{10}+4-\sqrt{90})(2\sqrt{10}+4-\sqrt{10})}$

Simplifying, we get  $A=\sqrt{(2\sqrt{10}+4)(2\sqrt{10}-4)(4-\sqrt{10})(4+\sqrt{10})}$

$\Rightarrow$  $A=\sqrt{24\times 6}=12$

Option D is correct answer.

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