Answer:
- Q(2/3, -1 2/3)
- R(1 1/3, 3 2/3)
Step-by-step explanation:
Let (a, b) represent the coordinates of point Q on line x -2y -4 = 0. Then we know that ...
a -2b -4 = 0
a -2b = 4
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If P is the midpoint of QR, then ...
R = 2P -Q = 2(1, 1) -(a, b) = (2 -a, 2 -b)
We know this point satisfies the equation for the other line:
x + y = 5
(2 -a) +(2 -b) = 5
a + b = -1 . . . . . . . . . . . rearrange to standard form
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To find the solution to these two equations, we can subtract the first from the second:
(a +b) -(a -2b) = (-1) -(4)
3b = -5
b = -5/3
a = -1 -1b = -1 -(-5/3) = 2/3
The point Q is (a, b) = (2/3, -5/3).
The point R is ...
R = (2 -a, 2 -b) = (2 -2/3, 2 -(-5/3)) = (4/3, 11/3)
The exact coordinates of Q and R are ...
Q(2/3, -5/3), R(4/3, 11/3)
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Comment on the GeoGebra solution
The points can be found by reflecting either line across point P. Where that reflected line intersects the other line is one of the points of interest. Of course, the other is its reflection in P. You may recognize the equation for line b' (hidden in the diagram) as matching the second equation we derived above.
