来自洪敏的问题
(x+y)+(2x+1/1*2y)+(3x+1/2*3y)+.+(9x+1/8*9y)当X=2,Y=9时,求代数式的值
(x+y)+(2x+1/1*2y)+(3x+1/2*3y)+.+(9x+1/8*9y)当X=2,Y=9时,求代数式的值
1回答
2020-12-11 03:34
(x+y)+(2x+1/1*2y)+(3x+1/2*3y)+.+(9x+1/8*9y)当X=2,Y=9时,求代数式的值
(x+y)+(2x+1/1*2y)+(3x+1/2*3y)+.+(9x+1/8*9y)当X=2,Y=9时,求代数式的值
(x+y)+(2x+1/1*2y)+(3x+1/2*3y)+.+(9x+1/8*9y)
=x(1+2+3+...9)+y{1+1/(1*2)+1/(2*3)+1/(3*4)+...1/(8*9)}
=x(1+9)*9/2+y{1+1-1/2+1/2-1/3+1/3-1/4+...1/8-1/9)}
=45x+y(2-1/9)
=45x+2y-y/9
=45*2+2*9-9/9
=90+18-1
=107