Prove:
∵AC⊥BD,
∴∠OBC+∠KCB=90,
∵M is the midpoint of∴ MC = mkbc province,
∴∠KCB=∠MKC,
∠∠AKH =∠MKC,
∴∠AKH=∠KCB,
And ∠KBC=∠KAH,
∴∠KAH+∠AKH=90,
∴KH⊥AD。