将y=-1/2x^2+2x+1向上平移2个单位,再向右平移3个单位就是所求
y-2=-1/2(x-3)^2+2(x-3)+1
y=-1/2x^2+3x-9/2+2x-6+1+2
y=-1/2x^2+5x-15/2