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From any point on the line (t+2)(x+y) =1...

From any point on the line `(t+2)(x+y) =1, t ne -2`, tangents are drawn to the ellipse `4x^(2)+16y^(2) = 1`. It is given that chord of contact passes through a fixed point. Then the number of integral values of 't' for which the fixed point always lies inside the ellipse is

A

0

B

1

C

2

D

3

Text Solution

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The correct Answer is:
To solve the problem step by step, we will break down the given information and derive the necessary equations. ### Step 1: Understand the given line and ellipse The line is given by the equation: \[ (t + 2)(x + y) = 1 \quad \text{for } t \neq -2 \] We can rewrite this as: \[ x + y = \frac{1}{t + 2} \] The ellipse is given by: \[ 4x^2 + 16y^2 = 1 \] ### Step 2: Find the chord of contact For a point \((\alpha, \beta)\) on the line, the chord of contact to the ellipse can be expressed as: \[ 4x\alpha + 16y\beta = 1 \] Substituting \(\beta = \frac{1}{t + 2} - \alpha\) into the chord of contact equation: \[ 4x\alpha + 16y\left(\frac{1}{t + 2} - \alpha\right) = 1 \] Expanding this gives: \[ 4x\alpha + \frac{16y}{t + 2} - 16y\alpha = 1 \] Rearranging terms: \[ (4x - 16y)\alpha + \frac{16y}{t + 2} - 1 = 0 \] ### Step 3: Identify the fixed point The chord of contact must pass through a fixed point. The coefficients of \(\alpha\) must equal zero for the line to pass through a fixed point: \[ 4x - 16y = 0 \quad \Rightarrow \quad x = 4y \] Substituting \(x = 4y\) into the equation gives: \[ \frac{16y}{t + 2} - 1 = 0 \quad \Rightarrow \quad 16y = t + 2 \quad \Rightarrow \quad y = \frac{t + 2}{16} \] Then substituting back to find \(x\): \[ x = 4y = \frac{4(t + 2)}{16} = \frac{t + 2}{4} \] Thus, the fixed point is: \[ \left(\frac{t + 2}{4}, \frac{t + 2}{16}\right) \] ### Step 4: Substitute fixed point into the ellipse equation We need this fixed point to lie inside the ellipse: \[ 4\left(\frac{t + 2}{4}\right)^2 + 16\left(\frac{t + 2}{16}\right)^2 < 1 \] Calculating this: \[ 4 \cdot \frac{(t + 2)^2}{16} + 16 \cdot \frac{(t + 2)^2}{256} < 1 \] Simplifying: \[ \frac{(t + 2)^2}{4} + \frac{(t + 2)^2}{16} < 1 \] Finding a common denominator: \[ \frac{4(t + 2)^2 + (t + 2)^2}{16} < 1 \] This simplifies to: \[ \frac{5(t + 2)^2}{16} < 1 \] Multiplying both sides by 16: \[ 5(t + 2)^2 < 16 \] Dividing by 5: \[ (t + 2)^2 < \frac{16}{5} \] ### Step 5: Solve the inequality Taking the square root: \[ -\sqrt{\frac{16}{5}} < t + 2 < \sqrt{\frac{16}{5}} \] This gives: \[ -4/\sqrt{5} < t + 2 < 4/\sqrt{5} \] Subtracting 2: \[ -\frac{4}{\sqrt{5}} - 2 < t < \frac{4}{\sqrt{5}} - 2 \] ### Step 6: Calculate the bounds for \(t\) Calculating the numerical bounds: \[ -\frac{4}{\sqrt{5}} \approx -1.79 \quad \Rightarrow \quad -1.79 - 2 \approx -3.79 \] \[ \frac{4}{\sqrt{5}} \approx 1.79 \quad \Rightarrow \quad 1.79 - 2 \approx -0.21 \] Thus, we have: \[ -3.79 < t < -0.21 \] ### Step 7: Find integral values of \(t\) The integral values of \(t\) in this range are: \[ -3, -2, -1 \] Since \(t \neq -2\), the valid integral values are: \[ -3, -1 \] ### Conclusion Thus, the number of integral values of \(t\) for which the fixed point always lies inside the ellipse is: \[ \boxed{2} \]

To solve the problem step by step, we will break down the given information and derive the necessary equations. ### Step 1: Understand the given line and ellipse The line is given by the equation: \[ (t + 2)(x + y) = 1 \quad \text{for } t \neq -2 \] We can rewrite this as: ...
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