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Question 45

Mathematics Scalar and Vector Products Hard

Let&nbsp;<span class="math-tex">\(\rm \vec{a}\)</span>, <span class="math-tex">\(\rm \vec{b}\)</span>&nbsp;and&nbsp;<span class="math-tex">\(\rm \vec{c}\)</span>&nbsp;be the position vectors of the three vertices A, B, C of a triangle respectively. Then the area of this triangle is given by:

(A) <span class="math-tex">\(\rm \dfrac{1}{2} (\vec{a}\times \vec{b})\vec{c}\)</span>
(B) <span class="math-tex">\(\rm \dfrac{1}{2} |\vec{a}\times \vec{b} + \vec{b} \times \vec{c}+\vec{c}\times \vec{a}|\)</span>
(C) <span class="math-tex">\(\rm | \vec{a}\times \vec{b} + \vec{b} \times \vec{c} + \vec{c} \times \vec{a} | \)</span>
(D) None of these
✓ Correct Answer: Option B Verified Solution

📘 Step-by-Step Solution & Detailed Explanation:

Two sides of the triangle are \(\vec{AB} = \vec{b} - \vec{a}\) and \(\vec{AC} = \vec{c} - \vec{a}\).

Area = \(\frac{1}{2}|(\vec{b} - \vec{a}) \times (\vec{c} - \vec{a})|\)

Expand: \(\vec{b} \times \vec{c} - \vec{b} \times \vec{a} - \vec{a} \times \vec{c} + \vec{a} \times \vec{a} = \vec{a} \times \vec{b} + \vec{b} \times \vec{c} + \vec{c} \times \vec{a}\)

Area = \(\frac{1}{2}|\vec{a} \times \vec{b} + \vec{b} \times \vec{c} + \vec{c} \times \vec{a}|\)

Answer: (B)

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