y=1/4x2求导可得y′=1/2x
切线的斜率k=f′(2)=1
过(2,1)处的切线的方程为y-1=x-2即x-y+1=0
切线的斜率k=f′(-2)=-1
过(-2,1)处的切线的方程为y-1=-x+2即x+y-3=0