Đáp án+Giải thích các bước giải:
Bài `3:`
`b) 2/3 + (-1/4) + 1/(21) + 1/(12)`
`= 2/3 - 1/4 + 1/(21)+1/(12)`
`= (2/3 + 1/(21)) + (1/(12) - 1/4)`
`= ((14)/(21)+1/(21)) + (1/(12) - 3/(12))`
`= (15)/(21) - 2/(12)`
`= 5/7 - 1/6`
`=(30)/(42) - 7/(42)`
`= (21)/(42)`
`=1/2`
Bài `4:`
`a) (16)/5 - x = 4/5 - 3/(10)`
`<=> (16)/5 - x = 1/2`
`<=> x = (16)/5 - 1/2`
`<=> x = (27)/(10)`
Vậy `x = (27)/(10)`
`b) x - 3/4 = 1/2`
`<=> x = 1/2 +3/4`
`<=> x = 2/4 + 3/4`
`<=> x = 5/4`
Vậy `x = 5/4`
`c) x + 8/(15) = (36)/(45)`
`<=> x + 8/(15) = 4/5`
`<=> x = 4/5 - 8/(15)`
`<=> x = (12)/(15) - 8/(15)`
`<=>x= 4/(15)`
Vậy `x= 4/(15)`
`d) 7/4 -(x+5/3) = (-12)/5`
`<=> x + 5/3 = 7/4 + (12)/5 `
`<=> x + 5/3 = (83)/(20)`
`<=> x = (83)/(20) - 5/3`
`<=> x = (149)/(60)`
Vậy ` x = (149)/(60)`
`e) x - [(17)/2 - ((-3)/7 + 5/3)] = -1/3`
`<=> x-((17)/2 + 3/7 - 5/3) = -1/3`
`<=> x - ((357)/(42) + (18)/(42) - (70)/(42)) = -1/3`
`<=> x- (305)/(42) = -1/3`
`<=> x = (-1)/3 + (305)/(42)`
`<=> x = (97)/(14)`
Vậy ` x = (97)/(14)`
`f) 9/2 - [2/3 - (x+7/4)] = (-5)/4`
`<=> 9/2 - (2/3 - x - 7/4)=-5/4`
`<=> 9/2 - 2/3 +x + 7/4 = -5/4`
`<=> (67)/(12) +x = -5/4`
`<=> x = (-5)/4 - (67)/(12)`
`<=> x = -(41)/6`
Vậy `x = -(41)/6`
