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The two opposite vertices of a square are (-1, 2) and (3, 2). Find the coordinates of the other two vertices.

Solution:

Let ABCD be a square with A(-1,2) and B(-1,2) (3,2). And Point O is the point where AC and BD intersect.

Now find the coordinates of the points B and D.

Step 1: Find coordinates of point O and distance between A and C.

As we know, the diagonals of a square are equal and bisect each other.

AC= √[(3 + 1)+ (2 – 2)2] = 4

The coordinates of O can be found using the formula below:

x = (3 – 1)/2 = 1 and y = (2 + 2)/2 = 2

So, O(1,2)

Step 2: Using the Pythagoras theorem find the side of the square

Let a be the square’s side, and AC = 4.

From the right angle triangle, ACD,

a = 2√2

As a result, each square’s side= 2√2

Step 3: Find coordinates of point D

AD and CD length measure are equated.

Assume D’s coordinate are (x1, y1)

AD = √[(x1 + 1)+ (y1 – 2)2]

When both sides are squared,

AD2 = (x1 + 1)+ (y1 – 2)2

In the same way, CD2  = (x1 – 3)+ (y1 – 2)2

Because all of the sides of a square are equal, therefore AD = CD

(x1 + 1)+ (y1 – 2)2 = (x1 – 3)+ (y1 – 2)2

x12 + 1 + 2x1 = x12 + 9 – 6x1

8x1 = 8

x1 = 1

By using the value of x, we can calculate the value of y1 as follows.

From step 2: each square’s side = 2√2

CD2 = (x1 – 3)+ (y1 – 2)2

8 = (1 – 3)+ (y1 – 2)2

8 = 4 + (y1 – 2)2

y1 – 2 = 2

y1 = 4

As a result, D = (1, 4)

Step 4: Find coordinates of point B

From the BOD line segment

B’s coordinates can be calculated using O’s coordinates, as follows:

We had already calculated as O = (1, 2)

Say B = (x2, y2)

For BD;

1 = (x2 + 1)/2

x= 1

And 2 = (y2 + 4)/2

=> y2 = 0

As a result, the coordinates of the required points are as B = (1,0) and D = (1,4)