Given triangle $ABC$ with vertices $A(2, 6)$, $B(2+2\sqrt{2}, 0, 4)$, and $C(2+2\sqrt{2}, 4, 4)$. We need to find the lengths of sides $AB$ and $AC$, and the measure of angle $\angle BAC$. Also, identify the type of triangle $ABC$.

Geometry3D GeometryDistance FormulaLaw of CosinesTrianglesIsosceles TriangleAngle Calculation
2025/6/24

1. Problem Description

Given triangle ABCABC with vertices A(2,6)A(2, 6), B(2+22,0,4)B(2+2\sqrt{2}, 0, 4), and C(2+22,4,4)C(2+2\sqrt{2}, 4, 4). We need to find the lengths of sides ABAB and ACAC, and the measure of angle BAC\angle BAC. Also, identify the type of triangle ABCABC.

2. Solution Steps

First, calculate the lengths of the sides ABAB and ACAC. The distance between two points (x1,y1,z1)(x_1, y_1, z_1) and (x2,y2,z2)(x_2, y_2, z_2) in 3D space is given by:
d=(x2x1)2+(y2y1)2+(z2z1)2d = \sqrt{(x_2 - x_1)^2 + (y_2 - y_1)^2 + (z_2 - z_1)^2}
The length of side ABAB is:
AB=((2+22)2)2+(06)2+(46)2=(22)2+(6)2+(2)2=8+36+4=48=43AB = \sqrt{((2+2\sqrt{2}) - 2)^2 + (0 - 6)^2 + (4 - 6)^2} = \sqrt{(2\sqrt{2})^2 + (-6)^2 + (-2)^2} = \sqrt{8 + 36 + 4} = \sqrt{48} = 4\sqrt{3}
The length of side ACAC is:
AC=((2+22)2)2+(46)2+(46)2=(22)2+(2)2+(2)2=8+4+4=16=4AC = \sqrt{((2+2\sqrt{2}) - 2)^2 + (4 - 6)^2 + (4 - 6)^2} = \sqrt{(2\sqrt{2})^2 + (-2)^2 + (-2)^2} = \sqrt{8 + 4 + 4} = \sqrt{16} = 4
Next, calculate the length of side BCBC:
BC=((2+22)(2+22))2+(40)2+(44)2=(0)2+(4)2+(0)2=16=4BC = \sqrt{((2+2\sqrt{2}) - (2+2\sqrt{2}))^2 + (4 - 0)^2 + (4 - 4)^2} = \sqrt{(0)^2 + (4)^2 + (0)^2} = \sqrt{16} = 4
Since AC=BC=4AC = BC = 4, the triangle is an isosceles triangle.
Now, we need to find the angle BAC\angle BAC. We can use the Law of Cosines:
BC2=AB2+AC22ABACcos(BAC)BC^2 = AB^2 + AC^2 - 2 \cdot AB \cdot AC \cdot \cos(\angle BAC)
42=(43)2+422434cos(BAC)4^2 = (4\sqrt{3})^2 + 4^2 - 2 \cdot 4\sqrt{3} \cdot 4 \cdot \cos(\angle BAC)
16=48+16323cos(BAC)16 = 48 + 16 - 32\sqrt{3} \cdot \cos(\angle BAC)
16=64323cos(BAC)16 = 64 - 32\sqrt{3} \cdot \cos(\angle BAC)
48=323cos(BAC)-48 = -32\sqrt{3} \cdot \cos(\angle BAC)
cos(BAC)=48323=323=3323=32\cos(\angle BAC) = \frac{-48}{-32\sqrt{3}} = \frac{3}{2\sqrt{3}} = \frac{3\sqrt{3}}{2 \cdot 3} = \frac{\sqrt{3}}{2}
BAC=arccos(32)=30\angle BAC = \arccos(\frac{\sqrt{3}}{2}) = 30^\circ
Since BAC=30\angle BAC = 30^\circ and AC=BCAC = BC, the other two angles are equal: ABC=BAC=(18030)/2=75\angle ABC = \angle BAC = (180^\circ - 30^\circ)/2 = 75^\circ.

3. Final Answer

AB=43AB = 4\sqrt{3}
AC=4AC = 4
BAC=30\angle BAC = 30^\circ
The triangle ABCABC is an isosceles triangle.

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