Special straight line method and so on.

Column:. F(x) is known as a linear function.

And f(f(x))=4X+3.

a*=4

Solution: let f (x) = ax+b.

Then f (x) = f (ax+b) = a (ax+b)+b = a * x+ab+b = 4x+3.

∴ab+b=3

The solution is a=2.

b= 1

or

a=-2

b=-3

The analytic formula of the original function is f(x)=2x+ 1.

Or f(x)=-2x-3.