Đáp án:
Giải thích các bước giải:
Bài 2:
`A=\frac{1/3-1/7-1/13}{2/3-2/7-2/13}.\frac{3/4-3/16-3/64-3/256}{1-1/4-1/16-1/64}+5/8`
`=\frac{7/21-3/21-1/13}{14/21-6/21-2/13}.(\frac{12/16-3/16-3/64-3/256}{4/4-1/4-1/16-1/64})+5/8`
`=\frac{4/21-1/13}{8/21-2/13}.(\frac{9/16-3/64-3/256}{3/4-1/16-1/64})+5/8`
`=\frac{52/273-21/273}{108/273-42/273}.(\frac{36/64-3/64-3/256}{12/16-1/16-1/64})+5/8`
`=\frac{31/273}{62/273}.(\frac{33/64-3/256}{11/16-1/64})+5/8`
`=\frac{31}{273}.(\frac{273}{62}).(\frac{132/256-3/256}{44/64-1/64})+5/8`
`=\frac{31}{62}.(\frac{129/256}{43/64})+5/8`
`=\frac{1}{2}.(\frac{129}{256}).(\frac{64}{43})+5/8`
`=\frac{1}{2}.\frac{3}{4}+5/8`
`=\frac{3}{8}+5/8`
`=8/8=1`
Vậy biểu thức `A=1`
Bài 3:
`a) 2/3x+5/7=3/10`
`<=>2/3x=3/10-5/7`
`<=>2/3x=21/70-50/70`
`<=>2/3x=-29/70`
`<=>x=-29/70:2/3`
`<=>x=-29/70.(3/2)`
`<=>x=-87/140`
Vậy `x=-87/140`
`b) 3/7+1/7:x=3/14`
`<=>14x.(3/7)+14.(1/7)=3x`
`<=>42/7x+14/7=3x`
`<=>6x+2=3x`
`<=>6x+2-3x=0`
`<=>3x+2=0`
`<=>x=(-2)/3`
Vậy `x=-2/3`
