Question

已知二次函数满足f(3x+1)=9(x)^2 - 6x +5 ,求f(x)

Answer 1

f(3x+1)=9(x)^2 - 6x +5 ,

3x+1=t

x=1/3(t-1)

f(t)=(t-1)^2-6[1/3(t-1)]+5

f(t)=t^2-4t+8

f(x)=x^2-4x+8