设方程为 a1x1+b1x2+c1x3=d1a2x1+b2x2+c2x3=d2a3x1+b3x2+c3x3=d3则 D=|(a1,b1,c1)(a2,b2,c2)(a3,b3,c3)|D1=|(d1,b1,c1)(d2,b2,c2)(d3,b3,c3)|D2=|(a1,d1,c1)(a2,d2,c2)(a3,d3,c3)|D3=|(a1,b1,d1)(a2,b2,d2)(a3,b3,d3)|x1=D1/D、x2=D2/D、x3=D3/D