M(-1,6) is the midpoint of RS. If S has the coordinates (3,13), find the coordinates of R. Multiple choice:
1) (7,-1)
2) (-5,20)
3) (7,20)
4) (-5,-1)

Question

M(-1,6) is the midpoint of RS. If S has the coordinates (3,13), find the coordinates of R. Multiple choice: 
1) (7,-1) 
2) (-5,20) 
3) (7,20) 
4) (-5,-1)

anonymous · Answer

( Sx + Rx ) / 2 = Mx
(Sy+Ry)/2 = My

Mx = -1
Sx + Rx = -2
Sx = 3
3 +Rx = -2
Rx = -5

My = 6
Sy+Ry = 12
Sy = 13
13 + Ry = 12
Ry = -1

R(-5,-1)

anonymous · Answer

why does Sx + Rx = -2?

anonymous · Answer

Ya i didnt understand that either

anonymous · Answer

(sx + rx) / 2 = Mx
(sx + rx) / 2 = -1

sx+rx = -2

anonymous · Answer

oh ok. i got it. (Sx+Rx)/2 = -1