根号（a²-5a+1）+根号（b²-4b+4）=0
a²-5a+1=0,b²-4b+4=0
a-5+1/a=0,b=2
a+1/a=5
（a²+1/a²）·b
=[(a+1/a)^2-2]*b
=23*2
=46