Question
Find the coordinates of the point which divides the line segment joining the points $(4, -3)$ and $(8, 5)$ in the ratio $3 : 1$ internally.

Answer


Let coordinates of the required point be $R(x, y)$. This means R divides the join of $P (4,-3)$ and $Q (8,5)$ in the ratio $3: 1$ internally.
Using the Section formula for internal division, here $x_1=4, y_1=-3, x_2=8, y_2=5, m=3, n=1$
$\Rightarrow(x,y) =$ $\left( \frac { mx _ { 2 } +n x _ { 1 } } { m+n} , \frac { m y _ { 2 } + ny _ { 1 } } { m+n } \right)$
$\Rightarrow(x,y) =$ ($\frac { 3 ( 8 ) + 1 ( 4 ) } { 3 + 1 }$,$\frac { 3 ( 5 ) + 1 ( - 3 ) } { 3 + 1 }$)
$\Rightarrow$ (x,y) = $( \frac { 24 + 4 } { 4 } , \frac { 15-3} { 4 })$
$\Rightarrow (x,y) = ( \frac { 28 } { 4 } , \frac { 12} { 4 }) =(7, 3)$
$\Rightarrow x= 7$ and $y= 3$
Thus, the coordinates of $R (x,y) = (7,3)$

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