Example 1 :
Name the type of quadrilateral formed. If any, by the following points and give reasons for your answer:
(4,5) (7,6) (4,3) (1,2)
Solution :
Let the given points as A(4, 5) B(7, 6) C(4, 3) and D (1, 2)
Distance between two points = √(x2 - x1)2 + (y2 - y1)2
Length of the side AB :
Here, x1 = 4, y1 = 5, x2 = 7 and y2 = 6
= √(7-4)2 + (6-5)2
= √3² + 1²
= √9 + 1
= √10
Length of the side BC :
Here, x1 = 7, y1 = 6, x2 = 4 and y2 = 3
= √(4-7)² + (3-6)²
= √(-3)² + (-3)²
= √9 + 9
= √18
Length of the side CD :
Here, x1 = 4, y1 = 3, x2 = 1 and y2 = 2
= √(1-4)2 + (2-3)2
= √(-3)2 + (-1)2
= √9 + 1
= √10
Length of the side DA :
Here, x1 = 1, y1 = 2, x2 = 4 and y2 = 5
= √(4-1)2 + (5-2)2
= √32 + 32
= √9 + 9
= √18
AB = CD, BC = DA. length of opposite sides are equal.
Length of AC :
Here, x1 = 4, y1 = 5, x2 = 4 and y2 = 3
= √(4-4)² + (3-5)²
= √0² + (-2)²
= √4
= 2
Length of BD :
Here, x1 = 7, y1 = 6, x2 = 1 and y2 = 2
= √(1-7)2 + (2-6)2
= √(-6)2 + (-4)2
= √36 + 16
= √52
It can be observed that opposite sides of this quadrilateral are of the same length.
Since the diagonals are of different lengths, the given points are the vertices of the parallelogram.
Example 2 :
Find the points on the x-axis which is equidistant from (2, -5) and (-2, 9)
Solution :
We have to find the point on x-axis. So its y-coordinate will be 0.
Let the point on x axis be (x, 0)
Distance between (x, 0) and (2, -5) =
Distance between (x, 0) and (-2, 9)
Distance between two points
= √(x2 - x1)2 + (y2 - y1)2
Here, x1 = x, y1 = 0, x2 = 2 and y2 = -5
= √(2 - x)2 + (5 - 0)2
= √(2 - x)2 + 25 ---------------(1)
Here, x1 = x, y1 = 0, x2 = -2 and y2 = 9
= √(-2-x)2 + (9-0)2
= √(2+x)2 + 92
= √(2+x)2 + 81
√(2 - x)2 + 25 = √(2 + x)2 + 81
Taking squares on both sides, we get
4 + x2 - 4 x + 25 = 4 + x2 + 4 x + 81
x² - x² - 4 x - 4 x + 4 - 4 = 81 - 25
-8 x = 56
x = -7
So, the required point is (-7, 0)
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