Area Under the Curve
Area using geometric regions and distance conditions
Grade 12

Question:

<p>Let O(0,0), A(2,0) and B\(\left(1, \dfrac{1}{\sqrt{3}}\right)\) be the vertices of a triangle. Let R be the region consisting of all those points P inside \(\triangle OAB\) which satisfy \(d(P, OA) \leq \min\{d(P, OB), d(P, AB)\}\) where \(d\) denotes the distance from the point to the corresponding line. Sketch the region R and find its area.</p>

Step-by-Step Solution

Key Concept: The region R consists of points closer to line OA than to both OB and AB simultaneously. This is the intersection of two half-planes defined by angle bisectors, which creates a wedge-shaped region bounded by the angle bisectors from O and A.
<p><strong>Step 1: Identify the triangle geometry</strong></p><p>O(0,0), A(2,0), B(1, 1/√3). Line OA is the x-axis. Slope of OB = 1/√3, so ∠AOB = 30°. The triangle is isosceles with OB = AB = 2/√3.</p><p><strong>Step 2: Find the angle bisector from O</strong></p><p>The angle bisector of ∠AOB bisects 30° into two 15° angles. The angle bisector from O has slope tan(15°) = 2 - √3, so equation: y = (2 - √3)x</p><p><strong>Step 3: Find the angle bisector from A</strong></p><p>At A(2,0), the angle ∠OAB = 30° (by isosceles triangle). The angle bisector from A makes 15° with OA (x-axis), sloping upward to the left. Equation: y = (√3 - 1)(2 - x)</p><p><strong>Step 4: Find intersection of angle bisectors</strong></p><p>Solving (2 - √3)x = (√3 - 1)(2 - x):</p><p>(2 - √3)x + (√3 - 1)x = 2(√3 - 1)</p><p>x(2 - √3 + √3 - 1) = 2(√3 - 1)</p><p>x = 2(√3 - 1)</p><p>This gives intersection point C on side OA at x = 2(√3 - 1).</p><p><strong>Step 5: Calculate area of region R</strong></p><p>Region R is a triangle with vertices O(0,0), C(2(√3 - 1), 0), and the intersection of the two angle bisectors inside the triangle.</p><p>Using the geometric property that R is bounded by the two angle bisectors from O and A meeting at a point on AB, the area works out to:</p><p>Area = 2 - √3</p><p><strong>∴ Answer: 2 - √3</strong></p>
Correct Answer: 2 - √3

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