Given:
The three vertices of a parallelogram are (-3,8), (4,5), (2,-5).
To find:
The fourth vertex of the parallelogram.
Solution:
Let the vertices of the parallelogram are A(-3,8), B(4,5), C(2,-5) and D(a,b).
We know that, diagonals of a parallelogram bisect each other. It means midpoints of both diagonals are same.
Midpoint formula:
[tex]Midpoint=\left(\dfrac{x_1+x_2}{2},\dfrac{y_1+y_2}{2}\right)[/tex]
Two diagonals of ABCD are AC and BD.
Midpoint of AC = Midpoint of BD
[tex]\left(\dfrac{-3+2}{2},\dfrac{8-5}{2}\right)=\left(\dfrac{4+a}{2},\dfrac{5+b}{2}\right)[/tex]
[tex]\left(\dfrac{-1}{2},\dfrac{3}{2}\right)=\left(\dfrac{4+a}{2},\dfrac{5+b}{2}\right)[/tex]
On comparing both sides, we get
[tex]\dfrac{4+a}{2}=\dfrac{-1}{2}[/tex]
[tex]4+a=-1[/tex]
[tex]a=-1-4[/tex]
[tex]a=-5[/tex]
And,
[tex]\dfrac{5+b}{2}=\dfrac{3}{2}[/tex]
[tex]5+b=3[/tex]
[tex]b=3-5[/tex]
[tex]b=-2[/tex]
Therefore, the coordinates of fourth vertex are (-5,-2).