If $(x, y)$ be on the line joining the two points $(1, -3)$ and $(-4, 2)$, prove that $x + y + 2 = 0$.


Given:

$(x, y)$ is on the line joining the two points $(1, -3)$ and $(-4, 2)$.

To do:

We have to prove that $x + y + 2 = 0$.

Solution:

We know that,

If the points $A, B$ and $C$ are collinear then the area of $\triangle ABC$ is zero.

Let $A(1, -3), B(x, y)$ and $C(-4, 2)$ be the vertices of $\triangle ABC$.

Area of a triangle with vertices $(x_1,y_1), (x_2,y_2), (x_3,y_3)$ is given by, 

Area of $\Delta=\frac{1}{2}[x_{1}(y_{2}-y_{3})+x_{2}(y_{3}-y_{1})+x_{3}(y_{1}-y_{2})]$

Therefore,

Area of triangle \( ABC=\frac{1}{2}[1(y-2)+x(2+3)+(-4)(-3-y)] \)

\( 0=\frac{1}{2}[y-2+x(5)-(-4)(3+y)] \)

\( 0(2)=(y-2+5x+12+4y) \)

\( 0=5x+5y+10 \)

\( 5(x+y+2)=0 \)

\( x+y+2=0 \)

Hence proved.

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Updated on: 10-Oct-2022

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