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Explanation:
Step 1)
Add up the given values to get -4+9 = 5
note that -4+9 is the same as 9+(-4) = 9-4
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Step 2) Divide the result from step 1 above by 2 to get
5/2 = 2.5
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The general midpoint formula is
C = (A+B)/2
where A and B are the endpoint values and C is the midpoint of segment AB. Points A,B,C are all on the same number line.
In this case, A = -4 and B = 9, so,
C = (A+B)/2
C = (-4+9)/2
C = 5/2
C = 2.5