AB^2=BC^2+AC^2-2(AC)(BC)cosC
5^2=BC^2+5^2-10(BC)cosC
BC=10cosC
AP^2=PC^2+AC^2-2(PC)(AC)cosC
AP^2=PC^2+25-(PC)(10cosC)
AP^2=PC^2+25-(PC)(BC)=PC^2+25-(PC)(BP+PC)=25-BPxPC
所以:AP^2+BPxPC=25
AB^2=BC^2+AC^2-2(AC)(BC)cosC
5^2=BC^2+5^2-10(BC)cosC
BC=10cosC
AP^2=PC^2+AC^2-2(PC)(AC)cosC
AP^2=PC^2+25-(PC)(10cosC)
AP^2=PC^2+25-(PC)(BC)=PC^2+25-(PC)(BP+PC)=25-BPxPC
所以:AP^2+BPxPC=25