Midpoint formula HELP?

Question

M(-2, -1) is the midpoint of RS(line segment). If S has coordinates of (2,4) find the coordinates of R...

i worked it out and i got that the coordinates of R are (2 -2) help please

im not sure about my answer

Answer 1

Midpoint formula: (where (x1, y1) and (x2, y2) are the endpoints of the segment)

x-coordinate = (x1 + x2)/2

y-coordinate = (y1 + y2)/2

x-coordinate of midpoint is -2 and x-coordinate of S is 2:

(x1 + x2)/ 2 = -2

(2 + x2)/2 = -2

2 + x2 = -4

x2 = -6

y-coordinate of midpoint is -1 and y-coordinate of S is 4:

(y1 + y2)/2 = -1

(4 + y2)/2 = -1

4 + y2 = -2

y2 = -6

ANSWER: R(-6, -6)

Answer 2

Consider a 2-D Cartesian-coordinate system:

midpoint M of a stright line RS is:

x-coordinate: Mx=(Rx+Sx)/2

y-coordinate: My=(Ry+Sy)/2

In your case:

Mx = -2 = (Rx+2)/2  --->  Rx = -6

My = -1 = (Ry+4)/2  --->  Ry = -6

Coordinates of R are (-6,-6)