(a+b)^2=a^2+2ab+b^2=8,(a-b)^2=a^2-2ab+b^2=4
两式相加
2a^2+2b^2=8+4=12
a^2+b^2=6
两式相减
4ab=8-4=4
ab=1
a+1/a=3
(a+1/a)^2=9
a^2+2+1/a^2=9
a^2+1/a^2=7
(a^2+1/a^2)^2=7^2
a^4+2+1/a^4=49
a^4+a^-4=47
(a+b)^2=a^2+2ab+b^2=8,(a-b)^2=a^2-2ab+b^2=4
两式相加
2a^2+2b^2=8+4=12
a^2+b^2=6
两式相减
4ab=8-4=4
ab=1
a+1/a=3
(a+1/a)^2=9
a^2+2+1/a^2=9
a^2+1/a^2=7
(a^2+1/a^2)^2=7^2
a^4+2+1/a^4=49
a^4+a^-4=47