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The centre of a circle is (x – 2, x + 1) and it passes through the points (4, 4). Find the value (or values) of x, if the diameter of the circle is of length 2 5 units .(a) 1 or 3 (b) –1 or 4 (c) 5 or 4 (d) 3 or –2 |
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Answer» (c) 5 or 4 Radius of the circle = Dist. between the centre and given pt. on the circle = \(\sqrt{(x-2-4)^2+(x+1-4)^2}\) = \(\sqrt{(x-6)^2+(x-3)^2}\) = \(\sqrt{x^2-12x+36+x^2-6x+9}\) = \(\sqrt{2x^2-18x+45}\) Given, diameter = 2√5 ⇒ radius = \(\frac12\times2\sqrt5 = \sqrt5\) ∴ \(\sqrt{2x^2-18x+45}\) = √5 ⇒ 2x2 – 18x + 45 = 5 ⇒ 2x2 – 18x + 40 = 0 ⇒ x2 – 9x + 20 = 0 ⇒ (x – 5) (x – 4) = 0 ⇒ x = 5 or 4 |
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