How does the resistance change when the copper wire is evenly stretched?

How does the resistance change when the copper wire is evenly stretched?

According to r = PL / s, when the copper wire is stretched, P is constant, l increases, s decreases, so r increases

What happens to the resistance of an iron manganese copper alloy wire after it is folded in half and twisted together

The resistance is quarter of the original
Calculation formula: r = ρ L / S
Where:
ρ is the resistivity of the material, in ohm meters (Ω. M)
L is the length in meters (m)
S is the sectional area in square meters (M2)

If you fold up a thin wire with uniform thickness, the resistance will be reduced

Half the length, twice the cross-sectional area and a quarter of the resistance

Why is it wrong to say that the resistance of a copper wire becomes smaller after it is evenly elongated

The resistance of a conductor is a property of the conductor itself, which is determined by the material, length and cross-sectional area of the conductor. When the material remains unchanged, (1) if the length remains unchanged, the smaller the cross-sectional area is, the greater the resistance is; (2) if the cross-sectional area remains unchanged, the longer the length is, the greater the resistance is, (2) The two changes of the copper wire will be a larger resistance, so the resistance of the copper wire will be larger