We are concern about the vector (x-x0, y-y0, z-z0)
equaling to 5.
This happens
when √(x-x0)^2 + (y-y0)^2 + (z-z0)^2 = 5
Square
both side:
(x-x0)^2
+ (y-y0)^2 + (z-z0)^2 = 25 , a sphere
Which you will
recognize as a circle of radius one centered at (x0, y0, z0)
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The weight is proportional to the price. So if 10lb cost $18.24, quarter as much (2.5lb) would cost four times less($18.24÷4=$4.56).
How much money in the account? that piece is a bit cut out
