翻译一道数学题.
ifUisacolumnvectorwithnelementsallunityshowthatforanym×nmatrixA,thematrixB=1/n×U×U'×AreplaceseachelementofAwithitscolumnaverage.Illustrateyouranswerif124
A=246
368
4810
我不会打大括号.凑合着看吧~.翻译这个题,顺便告诉我U究竟是什么.