WBJEE · Maths · Circle

Let \(A\) be the centre of the circle \(x^{2}+y^{2}-2 x-4 y-20=0 .\) Let \(B(1,7)\) and
\(D(4,-2)\) be two points on the circle such that tangents at \(B\) and \(D\) meet at \(C\). The area of the quadrilateral \(A B C D\) is

A \(150 \mathrm{sq}\) units
B 50 sq units.
C \(75 \mathrm{sq}\) units
D \(70 \mathrm{sq}\) units

Verified Solution

Answer & Solution

Correct Answer

(C) \(75 \mathrm{sq}\) units

Step-by-step Solution

Detailed explanation

Given, equation of circle is \[ x^{2}+y^{2}-2 x-4 y-20=0 \] Center \(\left(1,2\right).\) and radius \(=\sqrt{(1)^{2}+\left(2)^{2}+20\right.}=5\) Coordinate of intersecting point of tangents at \(B\) and \(D\) is \(C(06,7)\) Area of quadrilateral \(A B C D\)…

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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Let \(A\) be the centre of the circle \(x^{2}+y^{2}-2 x-4 y-20=0 .\) Let \(B(1,7)\) and \(D(4,-2)\) be two points on the circle such that tangents at \(B\) and \(D\) meet at \(C\). The area of the quadrilateral \(A B C D\) is

Step-by-step Solution

Let \(A\) be the centre of the circle \(x^{2}+y^{2}-2 x-4 y-20=0 .\) Let \(B(1,7)\) and
\(D(4,-2)\) be two points on the circle such that tangents at \(B\) and \(D\) meet at \(C\). The area of the quadrilateral \(A B C D\) is