If (x-a) is a factor of f(x)=4x^3-9x^2+6x+1, a could be a factor of +-1/4 - here 1 comes from constant term and 4 comes from the coefficient of highest power x^3.
Hence, a could be +-1/4, +-1/2 or +-1.
Further from factor theorem if (x-a) is a factor of f(x) then f(a)=0.
We know here that f(1)=2 and f(-1)=-18 and hence (x-1) and (x+1) are not the factors of f(x). Similarly
f(1/2)=4/8-9/4+3+1!=0 and f(-1/2)=-4/8+9/4-3+1!=0
f(1/4)=4/64-9/16+3/4+1!=0 andf(-1/4)=-4/64-9/16-3/4+1!=0
Hence f(x)=4x^3-9x^2+6x+1 does not have rational factors.