已知1/a+1/b+1/a+b=0,求(b/a)^2+(a/b)^2的值

来源:学生作业帮助网 编辑:六六作业网 时间:2024/11/22 06:36:45
已知1/a+1/b+1/a+b=0,求(b/a)^2+(a/b)^2的值已知1/a+1/b+1/a+b=0,求(b/a)^2+(a/b)^2的值已知1/a+1/b+1/a+b=0,求(b/a)^2+(

已知1/a+1/b+1/a+b=0,求(b/a)^2+(a/b)^2的值
已知1/a+1/b+1/a+b=0,求(b/a)^2+(a/b)^2的值

已知1/a+1/b+1/a+b=0,求(b/a)^2+(a/b)^2的值
1/a+1/b+1/(a+b)=0
(a+b)/(ab)=-1/(a+b)
(a+b)²=-ab
(b/a)²+(a/b)²
=(a⁴+b⁴)/(a²b²)
=[(a²+b²)²-2a²b²]/(a²b²)
=(a²+b²)²/(a²b²) -2
=[(a+b)²-2ab]²/(a²b²) -2
=[-ab-2ab)²/(a²b²) -2
=(-3ab)²/(a²b²) -2
=9a²b²/(a²b²) -2
=9-2
=7

设b/a=t
那么
1/a+1/(ta)+1/(a+ta)=(1+1/t+1/(1+t))(1/a)=0
所以1+1/t+1/(1+t)=0
化简得到:
t^2+1+3t=0
所以(t^2+1)^2=9t^2
即t^4+1+2t^2=9t^2
t^4+1=7t^2
同除以t^2
t^2+1/t^2=7
所以
(b/a)^2+(a/b)^2
=t^2+1/t^2
=7