Find the area of the triangle ABC, given the coordinates of the vertices A(2, 2, 6), B(2 + $2\sqrt{2}$, 0, 4), and C(2 + $2\sqrt{2}$, 4, 4).

Geometry3D GeometryVectorsCross ProductArea of Triangle
2025/6/24

1. Problem Description

Find the area of the triangle ABC, given the coordinates of the vertices A(2, 2, 6), B(2 + 222\sqrt{2}, 0, 4), and C(2 + 222\sqrt{2}, 4, 4).

2. Solution Steps

First, we find the vectors AB\vec{AB} and AC\vec{AC}.
AB=BA=(2+222,02,46)=(22,2,2)\vec{AB} = B - A = (2 + 2\sqrt{2} - 2, 0 - 2, 4 - 6) = (2\sqrt{2}, -2, -2)
AC=CA=(2+222,42,46)=(22,2,2)\vec{AC} = C - A = (2 + 2\sqrt{2} - 2, 4 - 2, 4 - 6) = (2\sqrt{2}, 2, -2)
Next, we find the cross product of these two vectors.
AB×AC=i^j^k^22222222=i^((2)(2)(2)(2))j^((22)(2)(2)(22))+k^((22)(2)(2)(22))\vec{AB} \times \vec{AC} = \begin{vmatrix} \hat{i} & \hat{j} & \hat{k} \\ 2\sqrt{2} & -2 & -2 \\ 2\sqrt{2} & 2 & -2 \end{vmatrix} = \hat{i}((-2)(-2) - (-2)(2)) - \hat{j}((2\sqrt{2})(-2) - (-2)(2\sqrt{2})) + \hat{k}((2\sqrt{2})(2) - (-2)(2\sqrt{2}))
=i^(4+4)j^(42+42)+k^(42+42)=8i^+0j^+82k^=(8,0,82)= \hat{i}(4 + 4) - \hat{j}(-4\sqrt{2} + 4\sqrt{2}) + \hat{k}(4\sqrt{2} + 4\sqrt{2}) = 8\hat{i} + 0\hat{j} + 8\sqrt{2}\hat{k} = (8, 0, 8\sqrt{2})
The magnitude of the cross product is
AB×AC=82+02+(82)2=64+0+642=64+128=192=643=83||\vec{AB} \times \vec{AC}|| = \sqrt{8^2 + 0^2 + (8\sqrt{2})^2} = \sqrt{64 + 0 + 64 \cdot 2} = \sqrt{64 + 128} = \sqrt{192} = \sqrt{64 \cdot 3} = 8\sqrt{3}
The area of the triangle ABC is half the magnitude of the cross product.
Area=12AB×AC=12(83)=43Area = \frac{1}{2} ||\vec{AB} \times \vec{AC}|| = \frac{1}{2}(8\sqrt{3}) = 4\sqrt{3}

3. Final Answer

The area of the triangle ABC is 434\sqrt{3}.

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