Respuesta :

sqdancefan

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Answer:

  b = (-5, 2)

Step-by-step explanation:

b = 2m - a = 2(1, -1) -(7, -4) = (2-7, -2+4)

b = (-5, 2)

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About the formula

The midpoint is given by the formula ...

  m = (a+b)/2

Solving for b gives ...

  b = 2m -a . . . as above