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Let S and S' are the foci of the ellipse...

Let S and S' are the foci of the ellipse `x=3+5 cos theta, y=-2+4sin theta`. If B is one of the ends of one of the latus rectum, then the area (in sq. units) of the triangle BSS' is equal to

A

`(24)/(5)`

B

`(48)/(5)`

C

`(12)/(5)`

D

`(64)/(5)`

Text Solution

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To solve the problem step-by-step, we will first derive the equation of the ellipse from the given parametric equations, find the foci, determine the coordinates of point B (one of the ends of the latus rectum), and finally calculate the area of triangle BSS'. ### Step 1: Derive the equation of the ellipse Given the parametric equations: \[ x = 3 + 5 \cos \theta \] \[ y = -2 + 4 \sin \theta \] We can express \(\cos \theta\) and \(\sin \theta\) in terms of \(x\) and \(y\): \[ \cos \theta = \frac{x - 3}{5} \] \[ \sin \theta = \frac{y + 2}{4} \] Using the identity \(\sin^2 \theta + \cos^2 \theta = 1\): \[ \left(\frac{x - 3}{5}\right)^2 + \left(\frac{y + 2}{4}\right)^2 = 1 \] This simplifies to: \[ \frac{(x - 3)^2}{25} + \frac{(y + 2)^2}{16} = 1 \] ### Step 2: Identify the center, semi-major axis, and semi-minor axis From the equation, we can identify: - Center: \((h, k) = (3, -2)\) - Semi-major axis \(a = 5\) (along the x-axis) - Semi-minor axis \(b = 4\) (along the y-axis) ### Step 3: Find the foci of the ellipse The distance \(c\) from the center to each focus is given by: \[ c = \sqrt{a^2 - b^2} = \sqrt{25 - 16} = \sqrt{9} = 3 \] Thus, the foci \(S\) and \(S'\) are located at: \[ S(3 - 3, -2) = (0, -2) \quad \text{and} \quad S'(3 + 3, -2) = (6, -2) \] ### Step 4: Find the coordinates of point B (end of the latus rectum) The latus rectum of an ellipse is vertical at the foci. The coordinates of the ends of the latus rectum can be found using: \[ \left(h \pm c, k \pm \frac{b^2}{a}\right) \] Calculating the y-coordinates: \[ \frac{b^2}{a} = \frac{16}{5} \] Thus, the coordinates of point B (one of the ends of the latus rectum) are: \[ B(0, -2 \pm \frac{16}{5}) = \left(0, -2 + \frac{16}{5}\right) \text{ or } \left(0, -2 - \frac{16}{5}\right) \] Calculating: \[ -2 + \frac{16}{5} = -\frac{10}{5} + \frac{16}{5} = \frac{6}{5} \] \[ -2 - \frac{16}{5} = -\frac{10}{5} - \frac{16}{5} = -\frac{26}{5} \] So, the coordinates of point B are: \[ B(0, \frac{6}{5}) \text{ or } B(0, -\frac{26}{5}) \] ### Step 5: Calculate the area of triangle BSS' The area \(A\) of triangle BSS' can be calculated using the formula: \[ A = \frac{1}{2} \times \text{base} \times \text{height} \] Here, the base \(SS'\) is the distance between the foci: \[ SS' = 6 - 0 = 6 \] The height is the vertical distance from point B to the line joining S and S': For \(B(0, \frac{6}{5})\): \[ \text{height} = \left| \frac{6}{5} - (-2) \right| = \left| \frac{6}{5} + \frac{10}{5} \right| = \left| \frac{16}{5} \right| = \frac{16}{5} \] Calculating the area: \[ A = \frac{1}{2} \times 6 \times \frac{16}{5} = \frac{48}{5} \] ### Final Answer The area of triangle BSS' is: \[ \boxed{\frac{48}{5}} \text{ square units} \]
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