Brad and Barb are trying to find the length of a line segment connecting two points, (x1, y1) and (x2, y2). Brad uses the formula

d =
(x2 - x1)2 + (y2 - y1)2
.

Barb uses a different formula, but still gets the right answer. Which formula COULD she have used?
A)
(x1 - x2)2 + (y1 - y2)2
B)
(x2 + x1)2 - (y2 + y1)2
C)
(x2 + x1)2 + (y2 + y1)2
D)
(x22 - x12) - (y22 - y12)

Question

Brad and Barb are trying to find the length of a line segment connecting two points, (x1, y1) and (x2, y2). Brad uses the formula 

d = 
	(x2 - x1)2 + (y2 - y1)2
.

Barb uses a different formula, but still gets the right answer. Which formula COULD she have used?
A)
 	(x1 - x2)2 + (y1 - y2)2
B)
 	(x2 + x1)2 - (y2 + y1)2
C)
 	(x2 + x1)2 + (y2 + y1)2
D)
 	(x22 - x12) - (y22 - y12)

saylilbaby · Answer

@mathstudent55 @quin100 @Hero @Secret-Ninja

saylilbaby · Answer

@jim_thompson5910 @e.mccormick

anonymous · Answer

He could have used A)
You make me sad.

secret-ninja · Answer

x1 - x2 = - (x2 - x1), and squaring either gives (x2 - x1)^2. 
Similarly for y1 and y2. 

Answer A.

anonymous · Answer

$(x_2-x_1)^2 = (x_1-x_2)^2$