# how to find coordinates of a point

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#1
1. The points A, B have coordinates (-1,2) (8,5)
I did this and got 1/3
b) find the equation of AB
I got y-2=1/3x-(-1)
c)The line AB is extended to the point C so that B is the midpoint of AC. Find the coordinates of C

The answer is (17,8) but I'm not sure how
0
8 months ago
#2
because B is the midpoint of AC, you know that AB=BC, so AC=2AB. You take the vector AB, which is (9,3), multiply it by 2 to get (18,6) and add it to A.

Alternatively, you can just add (9,3) to (8,5) for the same effect.
Last edited by Theloniouss; 8 months ago
1
#3
(Original post by Knortfoxx)
because B is the midpoint of AC, you know that AB=BC, so AC=2AB. You take the vector AB, which is (9,3), multiply it by 2 to get (18,6) and add it to A.

Alternatively, you can just add (9,3) to (8,5) for the same effect.
oh god, is that it? Thanks so much, I have no idea why I struggled with finding the coordinates so much
0
8 months ago
#4
(Original post by mpaprika)
oh god, is that it? Thanks so much, I have no idea why I struggled with finding the coordinates so much
No problem! Often the most obvious questions are the hardest.
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