midpoint

 

Given that M(1,-6) is the midpoint of AB and A(-2,-1) is one endpoint, what is the sum of the coordinates of point B?     

 

Visualize or, better yet, sketch the following on an x-y coordinate grid.     

 

From endpoint A (–2,–1) to midpoint M (+1,–6) you went right 3 and down 5.     

 

To get from the midpoint to endpoint B, move the same directions and amounts.     

 

For x, from +1 go right 3 to +4.  For y, from –6 go down 5 to –11.  B is at (+4,–11).     

 

Adding the coordinates of B   ——>>   (+4) + (–11)  =  –7 is their sum.     

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