Circles
Tangents and Director Circle
Grade 11
Question:
<p><strong>Statement-1:</strong> Tangents are drawn from the point <span class="math">\((17, 7)\)</span> to the circle <span class="math">\(x^2 + y^2 = 169\)</span>. The tangents are mutually perpendicular.<br/><strong>because</strong><br/><strong>Statement-2:</strong> The locus of the points from which mutually perpendicular tangents can be drawn to the given circle is <span class="math">\(x^2 + y^2 = 338\)</span>.</p>
<p>(a) Statement-1 is true, Statement-2 is true; Statement-2 is a correct explanation for Statement-1</p>
<p>(b) Statement-1 is true, Statement-2 is true; Statement-2 is not a correct explanation for Statement-1</p>
<p>(c) Statement-1 is true, Statement-2 is false</p>
<p>(d) Statement-1 is false, Statement-2 is true</p>
Step-by-Step Solution
Key Concept: For a point P to draw mutually perpendicular tangents to a circle, P must lie on the director circle (locus x² + y² = 2r²). We need to verify if (17,7) lies on this locus for the given circle and confirm both statements.
<p><strong>Step 1: Identify the circle parameters</strong></p><p>Given circle: x² + y² = 169</p><p>Here, r² = 169, so r = 13</p><p></p><p><strong>Step 2: Verify Statement-2 (the locus condition)</strong></p><p>For a circle x² + y² = r², the locus of points from which mutually perpendicular tangents can be drawn is the director circle: x² + y² = 2r²</p><p>For our circle: x² + y² = 2(169) = 338</p><p>Statement-2 is <strong>TRUE</strong></p><p></p><p><strong>Step 3: Verify Statement-1 by checking if (17,7) satisfies the director circle equation</strong></p><p>Substitute (17, 7) into x² + y² = 338:</p><p>17² + 7² = 289 + 49 = 338 ✓</p><p>Since (17, 7) lies on the director circle x² + y² = 338, tangents drawn from (17, 7) to the circle x² + y² = 169 are indeed <strong>mutually perpendicular</strong></p><p>Statement-1 is <strong>TRUE</strong></p><p></p><p><strong>Step 4: Determine the relationship</strong></p><p>Statement-2 explains why Statement-1 is true. The tangents from (17, 7) are perpendicular precisely because (17, 7) lies on the director circle, which is the complete locus of all points with this property.</p><p>Statement-2 is a <strong>correct explanation</strong> for Statement-1</p><p></p><p><strong>∴ Answer: (a) Statement-1 is true, Statement-2 is true; Statement-2 is a correct explanation for Statement-1</strong></p>
Correct Answer: a