In rectangle ABCD, take any point P, connect AP, BP, CP, DP, ask the relationship of AP, BP, CP, DP

In rectangle ABCD, take any point P, connect AP, BP, CP, DP, ask the relationship of AP, BP, CP, DP

PA^2+PC^2=PB^2+PD^2
Let p be above ad, PF through P, vertical ad to e, vertical BC to F
From Pythagorean theorem PA ^ 2 = PE ^ 2 + AE ^ 2
PC^2=PF^2+CF^2
PB^2=PF^2+BF^2
PD^2=PE^2+DE^2
AE = BF, ed = FC
Then PA ^ 2 + PC ^ 2 = Pb ^ 2 + PD ^ 2