1\ piecewise function, and substitute it into the corresponding analytical formula.

f(- 1)= f(- 1+3)= f(2)= f(2+3)= f(5)

=5-4= 1,

2，∫f(x)= CX/(2x+3)，

∴f[f(x)]=[c^2x/(2x+3)]/[2cx/(2x+3)+3]

=c^2x/(2cx+6x+9)

=x，

That is, c 2 = 9, 2c+6=0,

∴c=-3