Đáp án:
`↓↓`
Giải thích các bước giải:
`1)`
`a)`
`1995 × 1994 - 1/1993 × 1995 + 1994 `
`= 1995 ×1994 - 1/ ( 1994 - 1 ) × 1995 + 1994`
`= 1995 ×1994 - 1/ 1994 × 1995 - 1995 + 1994`
`= 1995 × 1994 - 1/ 1994 × 1995 - 1`
`= 1`
`b)`
`2/3 + 2/15 + 2/35 + 2/63`
`= 1/1 × 3 + 1/3×5 + 1/5 × 7 + 1/7 × 9`
`= 1 - 1/3 + 1/3 - 1/5 + 1/5 - 1/7 + 1/7 - 1/9 `
`= 1 - 1/9`
`= 8/9`
`2)`
`(1.1/4+1.1/2+1.3/4+2+2.1/4+2.1/2+2.3/4+ ...+4.3/4):23`
`=(1+1.1 +1.1+1.3+2+2.1+2.1+2.3+ ...+4.3):23`
`=( 1+1+1+3+2+2+6+...+12):23`
`=(2+4+4+6+...+12):23`
`=(6+10+...+12):23`
`=(16+...+12):23`
`=(16+12):23`
`=28:23`
`=28/23 .`
