由a+b+2c=1,a+b=1-2c∴(a+b)2=(1-2c)2∴a2+b2+2ab=1-4c+4c2…①又∵a2+b2-8c2+6c=5…②用①-②得:2ab=2c-4-4c2即ab=c-2-2c2∴ab-bc-ca=ab-c(a+b)=ab-c(1-2c)=c-2-2c2-c(1-2c)=-2.
46.a+b+2c = 1,a2 + b2-8c2+6c = 5則,ab-bc-..-阿摩線上測驗