If \(\mathrm{A}(6,4,6), \mathrm{B}(12,4,0), \mathrm{C}(4,2,-2)\) are the vertices of triangle, then it's incentre is (A) \([(22 / 3),(10 / 3),(4 / 3)]\) (B) \([\\{(-22) / 3\\}(10 / 3),(4 / 3)]\) (C) \([(22 / 3),\\{(-10) / 3\\},(4 / 3)]\) (D) \([(22 / 3),(10 / 3),\\{(-4) / 3\\}]\)

Short Answer

Expert verified
The short answer is: The incentre of the triangle is \(\left(\frac{22}{3}, \frac{10}{3}, \frac{4}{3}\right)\).

Step by step solution

01

Find the length of each side of the triangle

First, use the distance formula to find the length of each side of the triangle: \(AB\), \(BC\), and \(AC\). Distance formula: \(d = \sqrt{(x_2 - x_1)^2 + (y_2 - y_1)^2 + (z_2 - z_1)^2}\) For sides AB, BC, and AC, we have: \(AB = \sqrt{(12 - 6)^2 + (4 - 4)^2 + (0 - 6)^2} = \sqrt{6^2 + 6^2} = 6\sqrt{2}\) \(BC = \sqrt{(4 - 12)^2 + (2 - 4)^2 + (-2 - 0)^2} = \sqrt{8^2 + 2^2 + 2^2} = 2\sqrt{17}\) \(AC = \sqrt{(4 - 6)^2 + (2 - 4)^2 + (-2 - 6)^2} = \sqrt{2^2 + 2^2 + 8^2} = 2\sqrt{17}\)
02

Find the ratio in which the angle bisectors divide each other

Now, apply the angle bisector theorem to get the ratio: The ratio in which angle bisector at vertex A divides side BC: \(\frac{AB}{AC} = \frac{6\sqrt{2}}{2\sqrt{17}} = \frac{3\sqrt{2}}{\sqrt{17}}\) Similarly for vertex B, the ratio in which angle bisector at vertex B divides side AC: \(\frac{AB}{BC} = \frac{6\sqrt{2}}{2\sqrt{17}} = \frac{3\sqrt{2}}{\sqrt{17}}\) Now, let's find the coordinates of the point on the line segment BC where the angle bisector at vertex A intercepts, and similarly for the angle bisector at vertex B on the line segment AC.
03

Find the coordinates of the angle bisectors' interception points

We can find the coordinates of these interception points on sides BC and AC using the section formula, given the ratio obtained above. Section formula: \((x, y, z) = \left(\frac{mx_2 + nx_1}{m + n}, \frac{my_2 + ny_1}{m + n}, \frac{mz_2 + nz_1}{m + n}\right)\) For the angle bisector at vertex A, the point on side BC where it intercepts: \((x, y, z) = \left(\frac{\frac{3\sqrt{2}}{\sqrt{17}} \cdot 4 + \frac{\sqrt{17}}{\sqrt{17}} \cdot 12}{\frac{3\sqrt{2}}{\sqrt{17}} + \frac{\sqrt{17}}{\sqrt{17}}}, \frac{\frac{3\sqrt{2}}{\sqrt{17}} \cdot 2 + \frac{\sqrt{17}}{\sqrt{17}} \cdot 4}{\frac{3\sqrt{2}}{\sqrt{17}} + \frac{\sqrt{17}}{\sqrt{17}}}, \frac{\frac{3\sqrt{2}}{\sqrt{17}} \cdot (-2) + \frac{\sqrt{17}}{\sqrt{17}} \cdot 0}{\frac{3\sqrt{2}}{\sqrt{17}} + \frac{\sqrt{17}}{\sqrt{17}}}\right) = \left(\frac{22}{3}, \frac{10}{3}, \frac{4}{3}\right)\) Since the incentre is the point where the angle bisectors intersect, we can conclude that the incentre of the triangle is: \(\left(\frac{22}{3}, \frac{10}{3}, \frac{4}{3}\right)\) Therefore, the correct answer is (A).

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