5^2/1.6 + 5^2/6.11 +…..+ 5^2/26.31(tính nhanh)
x + 3/10 = 4/5
2/9 – 3.x = -4/3
(3/5 – x ) + 13/20 = 5/6
(2x – 1/2) =3/4
5^2/1.6 + 5^2/6.11 +…..+ 5^2/26.31(tính nhanh)
x + 3/10 = 4/5
2/9 – 3.x = -4/3
(3/5 – x ) + 13/20 = 5/6
(2x – 1/2) =3/4
1. `5^(2)/1.6+5^(2)/6.11+…+5^(2)/26.31`
`=5.[(1-1/6)+(1/6-1/11)+…+(1/21-1/26)+(1/26-1/31)]`
`=5.(1-1/31)`
`=5.30/31`
`=150/31`
2. `x+3/10=4/5`
`<=>x=4/5-3/10`
`<=>x=1/2`
Vậy `x=1/2`
3. `2/9-3.x=-4/3`
`<=>-3.x=-4/3-2/9`
`<=>-3.x=-14/9`
`<=>-3x=14/27`
Vậy `14/27`
4. `(3/5-x)+13/20=5/6`
`<=>3/5-x=11/60`
`<=>x=11/60-3/5`
`<=>-5/12`
Vậy `-5/12`
5. `2x-1/2=3/4`
`<=>2x=5/4`
`<=>x=5/8`
Vậy `x=5/8`
`#Study well`
Đáp án:
Giải thích các bước giải:
`a) 5. (5/(1. 6)+ 5/(6. 11)+…+ 5/(26. 31))`
`= 5. (1- 1/6+ 1/6- 1/11+…+ 5/26- 5/31)`
`= 5. (1- 1/31)`
`= 5. 30/31`
`= 150/31`
`b) x+ 3/10= 4/5`
`x= 4/5- 3/10`
`x= 8/10- 3/10`
`x= 5/10`
`x= 1/2`
`c) 2/9- 3. x= -4/3`
`3. x= 2/9- (-4/3)`
`3. x= 2/9- (-12/9)`
`3. x= 14/9`
`x= 14/9: 3`
`x= 14/9. 1/3`
`x= 14/27`
`(3/5- x)+ 13/20= 5/6`
`(3/5- x)= 5/6- 13/20`
`(3/5- x)= 50/60- 39/60`
`(3/5- x)= 11/60`
`x= 3/5- 11/60`
`x= 36/60- 11/60`
`x= 25/60`
`x= 5/12`
`2x- 1/2= 3/4`
`2x= 3/4+ 1/2`
`2x= 3/4+ 2/4`
`2x= 5/4`
`x= 5/4: 2`
`x= 5/4. 1/2`
`x= 5/8`