Big Ideas Math Integrated I, 2016
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Big Ideas Math Integrated I, 2016 View details
8. Coordinate Proofs
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Exercise 21 Page 644

To find the midpoint of a segment, we use the Midpoint Formula. However, how do you use this formula when the midpoint is known and we are looking for one of the endpoints?

Example Solution: (- k, - m) and (k,m).

Practice makes perfect

Let's draw an arbitrary segment through the origin where the coordinates of one endpoint is (k,m).

To find the midpoint of a segment, we use the Midpoint Formula: M(x_1+x_2/2, y_1+y_2/2). However, in this case we know the coordinates of the midpoint (0,0) and are looking for an endpoint. Therefore, the formula we have to use is M_x = x_1+x_2/2 and M_y = y_1+y_2/2 By substituting the midpoint and our known coordinate, (k,m), we can solve for the second endpoint.
M_x = x_1+x_2/2
0 = x_1+ k/2
â–Ľ
Solve for x_1
0= x_1+k
- k= x_1
x_1 = - k
We will do the same thing for M_y.
M_y = y_1+y_2/2
0 = y_1+ m/2
â–Ľ
Solve for y_1
0 = y_1+m
- m= y_1
y_1 = - m
The second endpoint is (- k, - m).