f(x-1)=x²-2x+3=x²-2x+1+2=(x-1)²+2x和x-1同样在定义域上取值，将x-1换成xf(x)=x²+2x+1和x同样在定义域上取值，将x换成x+1f(x+1)=(x+1)²+2=x²+2x+3
f(x-1)=x^2-2x+3=（x-1）²＋2所以令x-1为x＋1，即得f(x+1)=（x＋1）²＋2=x²＋2x＋3
