Question

The midpoint of RT is S(0.5, –6.25). One endpoint is T(–5.5, 2.75). What are the coordinates of R? (–4.5, –15.25) (6.5, –9.75) (–4.5, –9.75) (6.5, –15.25)

Answer 1

D, (6.5, -15.25) , JUST GOT IT CORRECT

Answer 2

The midpoint formula is this:$( x_{midpt} , y_{midpt})=( \frac{ x_{1} + x_{2} }{2} , \frac{ y_{1}+ y_{2} }{2} )$.  We have the coordinates of the midpoint and the coordinates of one of the endpoints, so our formula becomes:$(.5, -6.25)=( \frac{-5.5+ x_{2} }{2}, \frac{2.75+ y_{2} }{2})$.  Now group the x stuff together and solve for x2 and group the y stuff together and solve for y2, like this:$.5= \frac{-5.5+ x_{2} }{2}$. Multiply both sides by 2 to get 1=-5.5+x2.  Solve for x2 to get x2 = 6.5.  Do the same with the y stuff:$-6.25= \frac{2.75+ y_{2} }{2}$.  Multiply both sides by 2 to get-12.5=2.75+y2 and solving for y2 gives you -15.25.  So your answer is the last of your choices above. Phew!