# Find Coordinates of Point B

• Sep 28th 2008, 09:44 PM
magentarita
Find Coordinates of Point B
The midpoint M of line segment AB has coordinates (- 3,4). If point A is the origin, (00), what are the coordinates of point B.

MY WORK:

I used the distance formula to find the distance from point A to the midpoint. I found the distance to be 5 units from point A to the midpoint and of course, this means the distance to point B is 10 units. However, I was not able to find the coordinates of B. How do I find the coordinates of B without the need of graphing paper?

I also used the midpoint formula but got no where.

Thanks
• Sep 28th 2008, 10:00 PM
Jhevon
Quote:

Originally Posted by magentarita
The midpoint M of line segment AB has coordinates (- 3,4). If point A is the origin, (00), what are the coordinates of point B.

MY WORK:

I used the distance formula to find the distance from point A to the midpoint. I found the distance to be 5 units from point A to the midpoint and of course, this means the distance to point B is 10 units. However, I was not able to find the coordinates of B. How do I find the coordinates of B without the need of graphing paper?

hmm, ok

Quote:

I also used the midpoint formula but got no where.
really?

let (x,y) be the coordinates of B. then, by the midpoint formula:

$\displaystyle \bigg( \frac {x + 0}2, \frac {y + 0}2\bigg) = (-3,4)$

$\displaystyle \Rightarrow \frac x2 = -3$ and $\displaystyle \frac y2 = 4$
.
.
.
• Sep 29th 2008, 09:35 PM
magentarita
I see........
Quote:

Originally Posted by Jhevon
hmm, ok

really?

let (x,y) be the coordinates of B. then, by the midpoint formula:

$\displaystyle \bigg( \frac {x + 0}2, \frac {y + 0}2\bigg) = (-3,4)$

$\displaystyle \Rightarrow \frac x2 = -3$ and $\displaystyle \frac y2 = 4$
.
.
.

I did not place x and y in the midpoint formula. This is why I was not able to find the coordinates of B.

Thanks
• Oct 4th 2008, 04:24 AM
djmccabie
maybe im wrong but it looks like you dont need to use formula for this question. if you double the coordinates of the midpoint you should get point B (-6, 8)

then use the formula to check the answer.