1、(a+1)²-5a
=a²+2a+1-5a
=a²-3a+1
=0
2、因:a²-3a+1=0 得:a²+1=3a 两边同除以a得:
a+1/a=3 两边同时平方得:
(a+1/a)²=3² 展开得:
a²+2+1/a²=9
即:a²+1/a²=7
1、(a+1)²-5a
=a²+2a+1-5a
=a²-3a+1
=0
2、因:a²-3a+1=0 得:a²+1=3a 两边同除以a得:
a+1/a=3 两边同时平方得:
(a+1/a)²=3² 展开得:
a²+2+1/a²=9
即:a²+1/a²=7