Four points A, B, C and D form a quadrilateral. Prove that it is a rectangle if and only if for an arbitrary point P we have PA2+PC2=PB2+PD2.
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The freight elevator
Helping us to load
A kind of lift with capacity
That carries charges so many
Used for goods mainly
With operators who load only
Moving with traction or hydraulic mainly
It goes up and down
Bringing you from top to the ground