Hyperbola
Tangent to Hyperbola
Grade 11
Question:
<p>Equation of tangent to hyperbola <span class="math">\frac{xh}{a^2} - \frac{yk}{b^2} = 1\</span> at point <span class="math">P(h,k)\</span> touches the parabola at point <span class="math">(at^2, 2at)\</span></p>
Step-by-Step Solution
Key Concept: A common tangent to a hyperbola and parabola must satisfy both tangent conditions simultaneously.
<p><strong>Solution:</strong></p><p>Equation of tangent to hyperbola: <span class="math">y = mx \pm \sqrt{a^2m^2 - b^2}\</span></p><p>For the tangent to parabola <span class="math">y^2 = 4ax\</span>, we equate:</p><p><span class="math">a^2m^2 - b^2 = \frac{a^2}{m^2}\</span></p><p><span class="math">a^2m^4 - b^2m^2 - a^2 = 0\</span></p><p>Solving: <span class="math">m^2 = \frac{b^2 \pm \sqrt{b^4 + 4a^4}}{2a^2}\</span></p><p>∴ Answer is (b)</p>
Correct Answer: b