Giúp nình với mình cảm ơn rất nhìu

Đáp án:

Bài `1:`

`a, 5/12 - 3/(-16) -3/4`

`=29/48-3/4`

`=-7/48`

`b, 17/8 : (27/8+(-11)/2)`

`=17/8 : (-17)/8`

`=-1`

`c, 5/13+(-5)/7+(-20)/41+8/13+(-21)/41`

`=(5/13+8/13)+( (-20)/41+(-21)/41)+(-5)/7`

 `=1+(-1)+(-5)/7`

`=0+(-5)/7`

`=(-5)/7`

`d, (-2)/7. 5/11+(-2)/7. 6/11+60/(-35)`

`=(-2)/7(5/11+6/11)+(-12)/7`

`=(-2)/7. 1+(-12)/7`

`=(-2)/7+(-12)/7`

`=-2`

Bài `2:`

`a, x-1/4=2`

`x=2+1/4`

`x=9/4`

`b, 3x+3/4=7/12-1`

`3x+3/4=(-5)/12`

`3x=(-5)/12-3/4`

`3x=(-7)/6`

`x=(-7)/6 : 3`

`x=(-7)/18`

`c, 1/3(2x-1)=(-4)/15`

`2x-1=(-4)/15: 1/3`

`2x-1=(-4)/5`

`2x=(-4)/5+1`

`2x=1/5`

`x=1/5: 2`

`x=1/10`

`d, x/2+x/5=17/10`

`(5x)/(2.5)+(2x)/(5.2)=17/10`

`(5x)/10+(2x)/10=17/10`

`(5x+2x)/10=17/10`

`5x+2x=17`

`(5+2)x=17`

`7x=17`

`x=17:7`

`x=17/7`

Bài `3:`

`A=4/(1.2)+4/(2.3)+4/(3.4)+...+4/(2014.2015)`

`1/4 A=1/4 ( 4/(1.2)+4/(2.3)+4/(3.4)+...+4/(2014.2015))`

`1/4 A=4( 1/(1.2)+1/(2.3)+1/(3.4)+..+1/(2014.2015))`

`1/4 A=4 (1-1/2+1/2-1/3+1/3-1/4+...+1/2014-1/2015)`

`1/4 A=4(1-1/2015)`

`1/4 A=4. 2014/2015`

`1/4 A=8056/2015`

`A=8056/2015 . 4`

`A=32224/2015`