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Prove that if (X,ρ)(X,\rho) is a metric space, then the function d(x,y)=ρ(x,y)+1d(x,y)=\rho(x,y)+1 is also a metric on XX. In other words, the question is asking you to prove that if you take a metric space and add 11 to the distance between any two points in that space, the resulting function will also be a metric space.

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Q. Prove that if (X,ρ)(X,\rho) is a metric space, then the function d(x,y)=ρ(x,y)+1d(x,y)=\rho(x,y)+1 is also a metric on XX. In other words, the question is asking you to prove that if you take a metric space and add 11 to the distance between any two points in that space, the resulting function will also be a metric space.
  1. Non-negativity Property: To prove that d(x,y)=ρ(x,y)+1d(x,y) = \rho(x,y) + 1 is a metric on XX, we need to show that it satisfies the four properties of a metric:\newline11. d(x,y)0d(x,y) \geq 0 for all x,yx, y in XX (non-negativity)\newline22. d(x,y)=0d(x,y) = 0 if and only if x=yx = y (identity of indiscernibles)\newline33. d(x,y)=d(y,x)d(x,y) = d(y,x) for all x,yx, y in XX (symmetry)\newline44. XX00 for all XX11 in XX (triangle inequality)
  2. Identity of Indiscernibles Property: First, we check the non-negativity property. Since ρ\rho is a metric on XX, we know that ρ(x,y)0\rho(x,y) \geq 0 for all x,yx, y in XX. Therefore, d(x,y)=ρ(x,y)+1d(x,y) = \rho(x,y) + 1 will also be greater than or equal to 00 for all x,yx, y in XX, because adding 11 to a non-negative number keeps it non-negative.
  3. Symmetry Property: Next, we check the identity of indiscernibles property. For any xx in XX, we have ρ(x,x)=0\rho(x,x) = 0 because ρ\rho is a metric. Thus, d(x,x)=ρ(x,x)+1=0+1=1d(x,x) = \rho(x,x) + 1 = 0 + 1 = 1. This shows that d(x,x)0d(x,x) \neq 0, which is not exactly what we want. However, if xyx \neq y, then ρ(x,y)>0\rho(x,y) > 0, and so d(x,y)=ρ(x,y)+1>1d(x,y) = \rho(x,y) + 1 > 1. This means that d(x,y)=0d(x,y) = 0 if and only if XX00 is not satisfied because XX11 is never XX22. We have found a math error.

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