The radius of the circle passing through the foci of the ellipse \(\left(\mathrm{x}^{2} / 16\right)+\left(\mathrm{y}^{2} / 9\right)=1\) and having its centre \((0,3)\) is \(\ldots \ldots\) (a) 4 (b) 3 (c) \(\sqrt{12}\) (d) \((7 / 2)\)

Short Answer

Expert verified
The radius of the circle passing through the foci of the ellipse \(\left(\frac{x^2}{16}\right)+\left(\frac{y^2}{9}\right)=1\) and having its center at \((0, 3)\) is \(4\).

Step by step solution

01

Find the foci of the ellipse

The equation of the ellipse is given by \(\left(\mathrm{x}^{2} / 16\right)+\left(\mathrm{y}^{2} / 9\right)=1\). This is in the standard form for an ellipse with horizontal major axis: \(\frac{x^2}{a^2} + \frac{y^2}{b^2} = 1\), where \(a^2 = 16\) and \(b^2 = 9\). The distance between the center of the ellipse and each focus is given by \(c = \sqrt{a^2 - b^2}\). Calculate the value of \(c\): \(c = \sqrt{16 - 9}\) \(c = \sqrt{7}\) Now, we can find the coordinates of the foci. Since the ellipse has a horizontal major axis and is centered at the origin, the foci are located at \((-c, 0)\) and \((c, 0)\), or \((-\sqrt{7}, 0)\) and \((\sqrt{7}, 0)\).
02

Find the radius of the circle

The circle has its center at (0, 3), and we just found the coordinates of the foci to be \((-\sqrt{7}, 0)\) and \((\sqrt{7}, 0)\). Since the circle passes through both foci, the distance from its center to each focus is the radius. We will use the distance formula to find this radius: \(r = \sqrt{(x_2 - x_1)^2 + (y_2 - y_1)^2}\) Calculate the distance between the center of the circle and one of the foci, for example, \((\sqrt{7}, 0)\): \(r = \sqrt{(0 - \sqrt{7})^2 + (3 - 0)^2}\) \(r = \sqrt{7 + 9}\) \(r = \sqrt{16}\) \(r = 4\) So, the radius of the circle is 4, which corresponds to choice (a). #Answer#: (a) 4

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