一元二次方程，怎么用x1+x2和x1*x2化x1/x2 ?

Question

就像化x1²+x2²一样=(x1+x2)²-2*x1*x2

Answer 1

设x1/x2=s

x1+x2=a (1)
x1*x2=b (2)

(1)²-2(2)=x1²+x2²=a²-2b (3)
(3)/(2)=(x1²+x2²)/x1*x2=x1/x2+x2/x1=s+1/s=(a²-2b)/b

然后解方程s+1/s=(a²-2b)/b就可以得到s的值了，自己算吧本回答被提问者采纳

Answer 2

设x1+x2=a (1)
x1*x2=b (2)
(1)两边平方得 x1^2+2x1*x2+x2^2=a^2 (3)
(3)除以(2)得 x1/x2+2+x2/x1=a^2/b
设x1/x2=A A+2+1/A=a^2/b
解一元二次方程就可求得A的值

Answer 3

(x1+x2)/(x1x2)=x1/x2+x2/x1
把x1/x2+x2/x1设成t+1/t就可以解出来了.