Circles
Circle equation derivation
Grade 11
Question:
<p>From a figure with points O, P, Q, C, and M, given <span class="math inline">\(OP = 5\)</span>, <span class="math inline">\(OQ = 6\)</span>, <span class="math inline">\(OM = \frac{5}{2}\)</span>, and <span class="math inline">\(CM = 3\)</span>. Find <span class="math inline">\(OC^2\)</span> and determine the equation of a circle with centre <span class="math inline">\(\left(\frac{5}{2}, 3\right)\)</span>.</p>
Step-by-Step Solution
Key Concept: Use the Pythagorean theorem in the right triangle formed to find OC, then write the circle equation with the given centre and radius.
<p><strong>Step 1:</strong> In triangle OMC, use the Pythagorean theorem.</p><p><strong>Step 2:</strong> <span class="math inline">$OC^2 = OM^2 + MC^2$</span></p><p><strong>Step 3:</strong> <span class="math inline">$OC^2 = \left(\frac{5}{2}\right)^2 + (3)^2 = \frac{25}{4} + 9 = \frac{25 + 36}{4} = \frac{61}{4}$</span></p><p><strong>Step 4:</strong> Radius of the circle is <span class="math inline">$\sqrt{\frac{61}{4}} = \frac{\sqrt{61}}{2}$</span></p><p><strong>Step 5:</strong> Equation of circle: <span class="math inline">$\left(x - \frac{5}{2}\right)^2 + (y - 3)^2 = \frac{61}{4}$</span></p><p>∴ <span class="math inline">$\lambda = \frac{61}{4}$</span></p>
Correct Answer: 61/4