Question 32

Mathematics Trigonometric Equations Hard

If A, B and C is three angles of a&nbsp;&Delta;ABC, whose area is&nbsp;&Delta;. Let a, b and c be the sides opposite to the angles A, B and C respectively. If&nbsp;<span class="math-tex">\(s=\dfrac{a+b+c}{2}=6\)</span>, then the product&nbsp;<span class="math-tex">\(\dfrac{1}{3}s^2 (s-a)(s-b)(s-c)\)</span>&nbsp;is equal to &nbsp;

(A) 2&Delta;&nbsp;
(B) 2&Delta;<sup>2</sup>
(C) <span class="math-tex">\(\sqrt{2}\Delta\)</span>
(D) &Delta;<sup>2</sup>
✓ Correct Answer: Option B Verified Solution

📘 Step-by-Step Solution & Detailed Explanation:

1. Given Information: - The semi-perimeter \( s \) of the triangle is: \[ s = \frac{a + b + c}{2} = 6 \] - The area \( \Delta \) of the triangle is given by Heron's formula: \[ \Delta = \sqrt{s(s - a)(s - b)(s - c)} \] 2. Square Both Sides: To eliminate the square root, square both sides of the area formula: \[ \Delta^2 = s(s - a)(s - b)(s - c) \] 3. Multiply Both Sides by \( s \): Multiply both sides of the equation by \( s \): \[ s \times \Delta^2 = s \times s(s - a)(s - b)(s - c) \] \[ s \Delta^2 = s^2(s - a)(s - b)(s - c) \] 4. Multiply Both Sides by \( \frac{1}{3} \): Multiply both sides of the equation by \( \frac{1}{3} \): \[ \frac{1}{3} s \Delta^2 = \frac{1}{3} s^2(s - a)(s - b)(s - c) \] Given \( s = 6 \), substitute: \[ \frac{1}{3} \times 6 \Delta^2 = \frac{1}{3} \times 6^2 (s - a)(s - b)(s - c) \] \[ 2 \Delta^2 = \frac{1}{3} \times 36 (s - a)(s - b)(s - c) \] \[ 2 \Delta^2 = 12 (s - a)(s - b)(s - c) \] Therefore, the derived expression is: \[ \boxed{\frac{1}{3} s^2(s - a)(s - b)(s - c) = 2 \Delta^2} \]

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