If the points A(a, -11), B(5, b), C(2, 15) and D(1, 1) are the vertices of a parallelogram ABCD, find the values of a and b.
Given points are A(a, -11), B(5, b), C(2, 15) and D(1, 1) and let the intersection of diagonals be E(xm , ym )
It is given that □ABCD is a parallelogram.
By midpoint formula.
x = 
, y = 
We know that midpoint of parallelogram coincide.
∴ Midpoint of AC = Midpoint of BD
∴ (
, 
) = ( 
, 
)
∴ 
= 
and 
= 
∴a = 4 and b = 3
26