Question

已知函数f(x+2)=x2+3x,求f(x)

Answer 1

令t=x+2,则x=t-2

代入等式得：f(t)=(t-2)^2+3(t-2)

f(t)=t^2-4t+4+3t-6=t^2-t-2

因此f(x)=x^2-x-2