honeyselect吐舌:2/5*(3/4+2/5)怎样简算呀

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谢谢哦

2/5*(3/4+2/5)
=2/5*3/4+2/5*2/5
=3/10+4/25
=15/50+8/50
=23/50

2/5*(4/3+5/2)
=2/5*23/20
=46/100
=23/50

2/5*(3/4+2/5)
=3/10+4/25
=23/50

2/1*2*3+2/2*3*4+2/3*4*5+......+2/1999*2000*2001 3/2 2/3 5/4 4/5 () 1/(2/3)/(3/4)/(4/5)/(5/6)/(6/7)/(7/8) 找规律:2/4 3/6 5/8 7/9 ()/() ()/() 1+2/3+3/4+4/5+……+2005/2006＝？ 3/4-2x=5/8 x- 2x+1/4- 2-x/5>3/4- x-2/3 1/1*2+1/2*3+1/3*4+1/4*5+...+1/1999*2000 1/2+2/3+3/4+4/5+……99/100=? 1-1/2+2/3-3/4+4/5-.......-9/10=?