x²-5x-7=0x²-5x=7x²-5x+(5/2)²=7+(5/2)²[x-(5/2)]²=53/4x-(5/2)=±√(53/4)x-(5/2)=±(√53)/2x-(5/2)=(53)/2或 x-(5/2)=-(√53)/2x1=(5+√53)/2,x2=(5-√53)/2