y=log[1/2(x^2-2x+3)]
=-log[2(x^2-2x+3)]
=-[log2+log(x^2-2x+3)]
=-log2-log[(x-1)^2+2]
(x-)^2+2>=2
∴ log[(x-1)^2+2]>=log2=log2
∴y=-log2-log[(x-1)^2+2]