1·设f=ax+b,则f（f）=a*（ax+b）+b=a*ax+a*b+b=4x-1
所以a*a=4,a*b+b=-1推得a=2,b=-1/3或a=-2,b=1
2·f（x+1）=2(x-1)(x-1/2)=2(x+1-2)(x+1-3/2)
推得f（x)=2(x-2)(x-3/2)
3·设f=ax方+bx+c,-b/2a=2,(4ac-b方)/4a=16
由题意知当x=6时,f=0,有36a+6b+c=0,三式联立,