d^2= (7-1)^2 + (12-4)^2
d^2= 6^2+8^2= 36+64= 100
d=\sqrt{100} = 10
M= ((4+6)/2, (4+8)/2)
M= (5, 6)
(4+8/2)*5-1
first step divide in the parentheses
(4+4)*5-1
second step add in the parentheses
8*5-1
third step multiply
40-1
last step subtract
39
