Question 1094717
<br>Draw a rough sketch if it helps; but forget the formal midpoint formula or any other algebra and use common sense.<br>
Imagine starting at S, where you know the coordinates are (-1,5).  You walk along segment RS, and you reach the midpoint N, with coordinates (8,-3).<br>
You know you have reached the midpoint; that means you are halfway.  And that means the distance you have left to walk is the same as the distance you just walked.<br>
You just walked from a point with x coordinate -1 to a point with x coordinate 8; that is 9 units.  You need to go another 9 units in the x direction to get to the end of your walk, at point R.  8+9=17; the x coordinate of R is 17.<br>
Similarly, you just walked from a y coordinate of 5 to a y coordinate of -3, a change of -8.  You need to walk another -8 units in the y direction to reach R; the y coordinate of R is -3-8 = -11.<br>
R is (17,-11).<br>
All the words make this look like a lot of work.  But without the words, it's a lot faster than plugging numbers into some magic formula:<br>
x: from -1 to 8 is 9; 8 plus 9 more is 17  
y: from 5 to -3 is -8; -3 plus another -8 makes -11<br>
or...<br>
8-(-1) = 9; 8+9 = 17;
(-3)-5 = -8; -3-8 = -11