化简求值:(x+y)+(2x+1/2y)+(3x+1/6y)+.+(9x+1/72y) ,其中x=1,y=-9

化简求值:(x+y)+(2x+1/2y)+(3x+1/6y)+.+(9x+1/72y) ,其中x=1,y=-9
化简求值:(x+y)+(2x+1/2y)+(3x+1/6y)+.+(9x+1/72y) ,其中x=1,y=-9

化简求值:(x+y)+(2x+1/2y)+(3x+1/6y)+.+(9x+1/72y) ,其中x=1,y=-9
原式=x(1+2+3+……+9)+y(1+1/2+1/6+……+1/72)
=45x+y(2-1/2+1/2-1/3+……+1/8-1/9)
=45x+y(2-1/9),
x=1,y=-9时原式=45-9（2-1/9)=45-18+1=28.