2 + 25y2 = 400 if k is" - Step-by-step solution, answer key, and detailed explanation on MCA Prep."> 2 + 25y2 = 400 if k is" - Step-by-step solution, answer key, and detailed explanation on MCA Prep." /> 2 + 25y2 = 400 if k is" - Step-by-step solution, answer key, and detailed explanation on MCA Prep." />

Question 10

Mathematics Parabola Hard

The line 3x + 5y = k touches the ellipse 16x<sup>2</sup> + 25y<sup>2</sup> = 400 if k is

(A) <span class="math-tex">\(\pm \sqrt{5}\)</span>
(B) <span class="math-tex">\(\pm \sqrt{15}\)</span>
(C) <span class="math-tex">\(\pm {25}\)</span>
(D) <span class="math-tex">\(\pm {35}\)</span>
✓ Correct Answer: Option C Verified Solution

📘 Step-by-Step Solution & Detailed Explanation:

1. The given line is rewritten in slope-intercept form: \[ y = -\frac{3}{5}x + \frac{k}{5} \] So, the slope \( m = -\frac{3}{5} \) and the y-intercept is \( c = \frac{k}{5} \). \[\] 2. The ellipse equation is rewritten in standard form: \[ \frac{x^2}{25} + \frac{y^2}{16} = 1 \] Here, \( a^2 = 25 \) and \( b^2 = 16 \). \[\] 3. The condition for tangency states that for a line \( y = mx + c \) to be tangent to the ellipse \( \frac{x^2}{a^2} + \frac{y^2}{b^2} = 1 \), the relation: \[ c^2 = a^2 m^2 + b^2 \] must hold. \[\] 4. Substituting the values: \[ \left(\frac{k}{5}\right)^2 = 25 \times \left(\frac{3}{5}\right)^2 + 16 \] \[ \frac{k^2}{25} = 25 \times \frac{9}{25} + 16 \] \[ \frac{k^2}{25} = 9 + 16 = 25 \] \[ k^2 = 25 \times 25 = 625 \] \[ k = \pm 25 \] Thus, the correct value of \( k \) is \( \pm 25 \).

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