Explanation
A median of a triangle is a line segment that joins thevertex of a triangle to the midpoint of the opposite side.Mid point of two points $$ { (x }_{ 1 },{ y }_{ 1 }) $$ and $$ { (x }_{ 2 },{ y}_{ 2 }) $$ is calculated by the formula $$ \left( \frac { { x }_{ 1 }+{x }_{ 2 } }{ 2 } ,\frac { { y }_{ 1 }+y_{ 2 } }{ 2 } \right) $$Since AD is the median, this means, D is the mid point of BC. Using this formula, mid point of BC $$= \left( \frac { 7- 2 }{ 2 } ,\frac { 2 - 5 }{ 2 } \right) = (\dfrac {5}{2},\dfrac {-3}{2}) $$
Distance between two points $$\left( { x }_{ 1 },{ y }_{ 1 } \right) $$ and $$ \left( { x }_{ 2 },{ y }_{ 2 }\right) $$ can be calculated using the formula $$ \sqrt { \left( { x }_{ 2 }-{x }_{ 1 } \right) ^{ 2 }+\left( { y }_{ 2 }-{ y }_{ 1 } \right) ^{ 2 } } $$
Hence, length of AD $$ = \sqrt { \left( \dfrac { 5 }{ 2 } -3 \right) ^{ 2 }+\left( \dfrac { -3 }{ 2 } -4 \right) ^{ 2 } } =\sqrt { \dfrac { 1 }{ 4 } +\dfrac { 121 }{ 4 } } =\sqrt { \dfrac { 122 }{ 4 } } =\dfrac { \sqrt { 122 } }{ 2 } $$
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