1/TÍNH NHANH
1/3 : 5/4 + 1/3 : 5/6 + 2/9
-1/6 = 2/3 . (-3/4) + (-2) mũ 2/ 5
2/TÌM X
a/ 2 1/5 + 3/5 . x =3/4 ( 2 1/5 là hỗn số )
b/ 2/3 – 1/3 . (2x – 5 )= 3/2
3/ Tính giá trị biểu thức
a/ 13/ 25 + -7/17 +12/25 + -10/ 17 = 1/7
b/ -5/9 . 13/ 28 – 13/28 . 4/9 + 13/28
Bài 1.
`1/3 : 5/4 + 1/3 : 5/6 + 2/9`
`= 1/3 :(5/4+5/6)+2/9`
`=1/3 : 25/12 + 2/9`
`=4/25 +2/9`
`=86/225`
.
`-1/6 + 2/3 .(-3/4) + ((-2)^2)/5`
`=-1/6 + (-1/2) + 4/5`
`=-2/3 +4/5`
`=2/15`
Bài 2.
a) `2 1/5 + 3/5 .x =3/4`
`11/5 + 3/5 .x = 3/4`
`3/5 .x=3/4-11/5`
`3/5 .x=-29/20`
`x=-29/20: 3/5`
`x=-29/12`
b) `2/3 -1/3 .(2x-5) =3/2`
`-1/3 (2x+5)=5/6`
`2x+5=7/6`
`2x=-23/6`
`x=-23/12`
Bài 3.
a) `13/25 + (-7/17) +12/25 + (-10/17) +1/7`
`=(13/25 + 12/25) -(7/17+10/17) +1/7`
`=1-1+1/7`
`=1/7`
b) `-5/9 .13/28 -13/28 .4/9 +13/28`
`= 13/28 .(-5/9 -4/9+1)`
`=13/28 .0`
`=0`.
Đáp án:
Giải thích các bước giải:
Bài `1:`
`1/3 : 5/4 + 1/3 : 5/6 + 2/9`
`= 1/3 xx 4/5 + 1/3 xx 6/5 + 2/9`
`= 1/3 xx ( 4/5 + 6/5 ) + 2/9`
`= 1/3 xx 2 + 2/9`
`= 2/3 + 2/9 = 8/9`
$\\$
`-1/6 + 2/3 . (-3/4) + ((-2)^2)/5`
`= (-1/6) + (-1/2) + 4/5`
`= -2/3 +4/5 = 2/15`
Bài `2:`
`a)`
`2 1/5 + 3/5 . x =3/4`
`=> 11/5 + 3/5 . x = 3/4`
`=> 3/5 . x = 3/4-11/5`
`=> 3/5 . x = -29/20`
`=> x=-29/12`
Vậy `x=-29/12`
`b)`
`2/3 – 1/3 .(2x-5) = 3/2`
`=> 1/3 (2x-5) = 2/3 – 3/2`
`=> 1/3 (2x-5) = -5/6`
`=> 2x-5 = -5/2`
`=> 2x = 5/2`
`=> x = 5/4`
$\\$
Bài `3:`
`a)`
`13/25 + (-7/17) +12/25 + (-10/17) +1/7`
`=(13/25 + 12/25) -(7/17+10/17) +1/7`
`=1-1+1/7=1/7`
`b)`
`-5/9 . 13/28 -13/28 . 4/9 + 13/28`
`= 13/28 .[(-5/9) + (-4/9) + 1 ]`
`= 13/28 .0 = 0`