Moving the bead across the center flips the restoring direction. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
A bead on the other side changes the sign
The bead is at negative 2 metres, so its signed displacement is negative 2 metres.
−2−0=−2
The restoring arrow reverses direction
With the same stiffness 2 newtons per metre, the force magnitude is 4 newtons toward positive position.