if you are given an endpoint and the midpoint how do you find the coordinates of the other endpoint

Question

Point C(3,8) is the midpoint of line segment AB. One endpoint is A(-1,5). find the coordinates of endpoint B.

 

Answer 1

C (3,8)

A(-1,5)

 

let point B(x,y)

 

(-1 + x)/2 = 3 ----->-1/2 + x/2 = 3  ----->x/2 = 3 + 1/2  ---->x = 7

(5 + y)/2 = 8  ------> 5/2 + y/2 = 8 ------>y/2 = 8 - 5/2  -----> y = y = 16 - 5 = 11

 

so, x = 7, y = 11