Ellipse
Tangent and Foci
Grade 11

Question:

<p><strong>Question 647</strong><br>Consider, \(E : \dfrac{(x-1)^2}{16} + \dfrac{(y-2)^2}{9} = 1\) and \(H : (x-1)^2 - (y-2)^2 = \dfrac{7}{2}\).<br><br>(Refer to the match the column table for questions 644–648.)<br><br>Which of the following options is the only <strong>correct</strong> combination?</p>
<p>(a) (II) (iv) (P)</p>
<p>(b) (III) (iii) (P)</p>
<p>(c) (III) (i) (R)</p>
<p>(d) (IV) (ii) (R)</p>

Step-by-Step Solution

Key Concept: The ellipse and hyperbola share the same center (1,2). To find intersection points, substitute the hyperbola equation into the ellipse equation by expressing one squared term in terms of the other using the hyperbola's constraint.
Step 1: Identify the common center of the ellipse and hyperbola. The given equation for the ellipse is $E : \dfrac{(x-1)^2}{16} + \dfrac{(y-2)^2}{9} = 1$. The given equation for the hyperbola is $H : (x-1)^2 - (y-2)^2 = \dfrac{7}{2}$. Both equations are of the form $\dfrac{(x-h)^2}{a^2} + \dfrac{(y-k)^2}{b^2} = 1$ and $\dfrac{(x-h)^2}{a^2} - \dfrac{(y-k)^2}{b^2} = 1$ respectively, where $(h,k)$ is the center. For both curves, the center is $(1, 2)$. Step 2: Express $(x-1)^2$ in terms of $(y-2)^2$ from the hyperbola equation. From the equation of the hyperbola $H$: $$(x-1)^2 - (y-2)^2 = \frac{7}{2}$$ Rearranging to isolate $(x-1)^2$, we get: $$(x-1)^2 = (y-2)^2 + \frac{7}{2}$$ Step 3: Substitute the expression for $(x-1)^2$ into the ellipse equation. Substitute $(x-1)^2 = (y-2)^2 + \frac{7}{2}$ into the equation of the ellipse $E$: $$\frac{(y-2)^2 + \frac{7}{2}}{16} + \frac{(y-2)^2}{9} = 1$$ Step 4: Solve the resulting equation for $(y-2)^2$. To eliminate the denominators, multiply the entire equation by the least common multiple of 16 and 9, which is 144: $$144 \left( \frac{(y-2)^2 + \frac{7}{2}}{16} + \frac{(y-2)^2}{9} \right) = 144 \times 1$$ $$9 \left( (y-2)^2 + \frac{7}{2} \right) + 16 (y-2)^2 = 144$$ Expand the terms: $$9(y-2)^2 + \frac{63}{2} + 16(y-2)^2 = 144$$ Combine the terms involving $(y-2)^2$: $$25(y-2)^2 + 31.5 = 144$$ Subtract 31.5 from both sides: $$25(y-2)^2 = 144 - 31.5$$ $$25(y-2)^2 = 112.5$$ Divide by 25: $$(y-2)^2 = \frac{112.5}{25}$$ $$(y-2)^2 = 4.5 = \frac{9}{2}$$ Taking the square root of both sides: $$y-2 = \pm\sqrt{\frac{9}{2}} = \pm\frac{3}{\sqrt{2}}$$ Step 5: Determine the values for $(x-1)^2$. Substitute $(y-2)^2 = \frac{9}{2}$ back into the expression for $(x-1)^2$ from Step 2: $$(x-1)^2 = (y-2)^2 + \frac{7}{2}$$ $$(x-1)^2 = \frac{9}{2} + \frac{7}{2}$$ $$(x-1)^2 = \frac{16}{2}$$ $$(x-1)^2 = 8$$ Taking the square root of both sides: $$x-1 = \pm\sqrt{8} = \pm 2\sqrt{2}$$ Step 6: Determine the number of intersection points and match with the given options. From $y-2 = \pm\frac{3}{\sqrt{2}}$, we have two distinct values for $y$. From $x-1 = \pm 2\sqrt{2}$, we have two distinct values for $x$. Combining these, there are $2 \times 2 = 4$ distinct points of intersection between the ellipse and the hyperbola. The coordinates of these intersection points are $(1 \pm 2\sqrt{2}, 2 \pm \frac{3}{\sqrt{2}})$. The existence of four distinct intersection points means that option (d) (IV) (ii) (R) is the correct combination. The final answer is $\boxed{\text{D}}$.
Correct Answer: D

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