(1?2)*(1?2)*(19?2)=1992 填运算符号 急用,急用!

( 1+17/1)*(1+17/2)*(1+17/3)*.*(1+17/19)/(1+19/1)*(1+19/2)*(1+19/30*.*(1+19/17)=? 1/1*2+1/2*3+.1/18*19+1/19*20=? 19题1、2 20-19+18-17+.2-1=? 1+2+3.+18+19+20= 9/2减19/1=多少? (19-2x)/5=x+1 2/1*3+2/3*5+2/5*7+.+2/17*19+2/19*21=? 因为1/1*3=1/2*（1-1/3）,1/3*5=1/2*(1/3-1/5),1/5*7=1/2*(1/5-1/7),.,1/17*19=1/2*(1/17-1/19)所以1/1*3+1/3*5+1/5*7+...+1/17*19=1/2*(1-1/3)+1/2*(1/3-1/5)+1/2*(1/5-1/7)+...+1/2*(1/17-1/19)=1/2*(1-1/3+1/3-1/5+1/5-1/7+...+1/17-1/19)=1/2*(1-1/19)=9/19(1 1/1*2+1/2*3+1/3*4...1/19*20=? 数学白痴提问(1/1*2)+(1/2*3)+(1/3*4)+.+(1/19*20)=? (1+19/105*1)+(1+19/105*2)+(1+19/105*3)+.+(1+19/105*19)+(1+19/105*20) 1/1*3=1/2（1-1/3）1/3*5=1/2（1/3-1/5）1/5*7=1/2（1/5-1/7）.1/17*19=1/2（1/17-1/19）所以1/1*3+1/3*5+1/5*7+.1/17*19=1/2（1-1/3）+1/2（1/3+1/5）+1/2（1/5-1/7）+.1/2（1/17-1/19）=1/2（1-1/3+1/3-1/5+1/5-1/7+1/7.+1/17-1/19）=1/2（1-1/1 1/1x3=1/2(1-1/3),1/3x5=1/2(1/3-1/5),1/5x7=1/2(1/5-1/7),……,1/17x19=1/2(1/17-1/19).∴1/1x3+1/3x5+1/5x7+……+1/17x19=1/2(1-1/3)+1/2(1/3-1/5)+1/2(1/5-1/7)+……+1/2(1/17-1/19)=1/2 (1-1/3+1/3-1/5+1/5-1/7+……+1/17-1/19)=1/2(1-1/19)=9/19根据以 13/19+1/2-13/19 (简算) 13/19+1/2-13/19 (简算) 21.4{3[2(x+1)-7]-19}-7=1 2/1+19/12×3.8