The vertices of the triangle are A(5, 4, 6), B(1, -1, 3) and C(4, 3, 2). The internal bisector of angle A meets BC at D. Find the coordinates of D and the length AD.
The vertices of the triangle are A(5, 4, 6), B(1, -1, 3) and C(4, 3, 2). The internal bisector of angle A meets BC at D. Find the coordinates of D and the length AD.

Given:

The vertices of the triangle are

    \[A\text{ }\left( 5,\text{ }4,\text{ }6 \right),\text{ }B\text{ }\left( 1,\text{ }-1,\text{ }3 \right)\text{ }and\text{ }C\text{ }\left( 4,\text{ }3,\text{ }2 \right)\]

By using the formulas let us find the coordinates of

    \[D\]

and the length of

    \[AD\]

The distance between any two points

    \[\left( a,\text{ }b,\text{ }c \right)\text{ }and\text{ }\left( m,\text{ }n,\text{ }o \right)\]

is given by,

RD Sharma Solutions for Class 11 Maths Chapter 28 – image 41

The section formula is given as

RD Sharma Solutions for Class 11 Maths Chapter 28 – image 42

RD Sharma Solutions for Class 11 Maths Chapter 28 – image 43 

    \[AB\text{ }:\text{ }AC\text{ }=\text{ }5:3\]

    \[BD:\text{ }DC\text{ }=\text{ }5:3\]

So,

    \[m\text{ }=\text{ }5\text{ }and\text{ }n\text{ }=\text{ }3\]

    \[B\left( 1,\text{ }-1,\text{ }3 \right)\text{ }and\text{ }C\left( 4,\text{ }3,\text{ }2 \right)\]

Coordinates of

    \[D\]

using section formula:

RD Sharma Solutions for Class 11 Maths Chapter 28 – image 44

RD Sharma Solutions for Class 11 Maths Chapter 28 – image 45

RD Sharma Solutions for Class 11 Maths Chapter 28 – image 46