计算①1x2/1+2x3/1+3x4/1+```+19x20/1= ②1x4/1+4x7/1+7x10/1+```+91

来源：学生作业帮编辑：大师作文网作业帮分类：数学作业时间：2024/11/11 10:32:26

计算①1x2/1+2x3/1+3x4/1+```+19x20/1= ②1x4/1+4x7/1+7x10/1+```+91x94/1=

是否写反了
差/(小*大) =1/小 - 1/大如 7/(3*10)=1/3 - 1/10 ; 1/(4*5)=1/4 - 1/5
但 1/(4*7) =3/(4*7) *(1/3)=(1/3)[1/4 -1/7]
1/(1*2)+1/(2*3)+1/(3*4)+...+1/(19*20)=1/1 -1/2+ 1/2 - 1/3 +1/3 - 1/4 +...+1/18- 1/19+1/19 -1/20
=1/1 -1/20 = 19/20...ANS
速算大分子=各项分子和=1*19=19 ;大分母=第一项分母头*最后项分母尾=1*20=20 =>19/20
1,4,7,...,91等差项数=(91-1)/3 +1=31
1/(1*4)+1/(4*7)+1/(7*10)+.+1/(91*94) =[1*31]/(1*94)=31/94...ANS
OR =1/3[1/1 - 1/4 +1/4 -1/7 +...+1/88- 1/91+1/91-1/94]=(1/3)(1- 1/94) =31/94

计算①1x2/1+2x3/1+3x4/1+```+19x20/1= ②1x4/1+4x7/1+7x10/1+```+91 (2X2)/1X3+(4X4)/(3X5)+(6X6)/(5X7)+...+(20X20)/(19X21)==? 已知:x1=1/2+1/3,x2=1/3+1/4,x3=x2+x1,x4=x3+x2.,x10=x9+x8,求：x7/x 计算：1/1x2+1/2x3+1/3x4+1/4x5+1/5x6+1/6x7+1/7x8+1/8x9+1/9x10. x8+x7+x6+x5+x4+x3+x2+x+1因式分解 2x2/1x3+4x4/3x5+6x6/5x7+8x8/7x9+10x10/9x11+12x12/11x13 仔细看看 100x( 3/1x4 + 3/4x7 +3/7x10 +.3/97x100)=?注：1x4、4x7、7x10等均为分母写清计算过程）1x2分之1-2x3分之1-3x4分之1-...-9x10分之1=1x3分之2+3x5分之2+5x7分之2 X1+2X2-X3+X4=1 计算1/1x4+1/4x7+1/7x10+.+1/2002x2005+1/2005x2008 计算1/1x4+1/4x7+1/7x10+***+1/2007x2010 计算:1x4分之一+4x7分之一+7x10分之一+10x13分之一+13x16分之一