Question 1207018
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If km refers to kilometers, then,
x = 2
4x^2-1 = 4(2)^2-1 
= 4*(4)-1 
= 16-1 
= 15


Summary:
x = 2 kilometers leads to 4x^2-1 = 15 kilometers


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If km in 2km doesn't refer to kilometers, and instead the k and m are separate variables, then:
x = 2km
4x^2-1 = 4(2km)^2-1
= 4(2^2k^2m^2)-1
= 4(4k^2m^2)-1
= 16k^2m^2-1


Summary:
x = 2km leads to 4x^2-1 = 16k^2m^2-1
if the "km" doesn't refer to kilometers but instead two different variables.
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