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bài `2`
`a, x-1/2 =-3/4`
`=> x=-3/4 +1/2`
`=> x=-3/4 +2/4`
`=> x= -1/4`
`b, x+1/6 =-3/8`
`=> x=-3/8 - 1/6`
`=>x= -13/24`
`c, x-2/3 =3/5 -1/4`
`=> x-2/3 =7/20`
`=>x= 7/20 +2/3`
`=>x= 61/60`
`d, x-1/4 = 5/8 . 2/3`
`=> x-1/4 =5/12`
`=>x= 5/12 +1/4`
`=>x= 5/12 + 3/12`
`=>x= 2/3`
`e, 4/5 -x=-8/35`
`=>x= 4/5-(-8/35)`
`=>x= 4/5+8/35`
`=>x= 36/35`
`f, 11/12 x +3/4=1/6`
`=> 11/12 x =1/6-3/4`
`=> 11/12 x =-7/12`
`=>x=-7/12 : 11/12`
`=>x=-7/12 xx 12/11`
`=>x= -7/11`
`g, 2/9 - 2/7 x= 1/3`
`=> 2/7 x= 2/9- 1/3`
`=> 2/7 x=-1/9`
`=>x=-1/9 : 2/7`
`=>x=-1/9 xx 7/2`
`=>x= -7/18`
`h, x + (-7/15) = -1 1/20`
`=> x + (-7/15) =-21/20`
`=>x= -21/20 - (-7/15)`
`=>x= -21/20+7/15`
`=>x=-7/12`
`i, 3 1/5 x -7/10 = 1 3/5`
`=> 16/5 x -7/10 =8/5`
`=> 16/5 x =8/5 + 7/10`
`=> 16/5 x =23/10`
`=>x= 23/10 : 16/5`
`=>x= 23/10 xx 5/16`
`=>x= 23/32`
`b, x -1/2 = 3/4 : 3/2`
`=> x -1/2 = 3/4 xx 2/3`
`=> x -1/2 = 1/2`
`=>x= 1/2+1/2`
`=>x=1`
`k , 4/5 -1/2 x=1/10`
`=> 1/2 x=4/5 -1/10`
`=>1/2 x=7/10`
`=>x= 7/10 :1/2`
`=>x= 7/10 xx 2`
`=>x=7/5`
Bài 1.
\(a,\dfrac{1}{3}+\dfrac{1}{4}=\dfrac{4}{12}+\dfrac{3}{12}=\dfrac{7}{12}\)
\(b,\dfrac{-2}{5}+\dfrac{7}{21}=\dfrac{-42}{105}+\dfrac{35}{105}=\dfrac{-77}{105}=\dfrac{-11}{15}\)
\(c,\dfrac{3}{8}+\dfrac{-5}{6}=\dfrac{18}{48}+\dfrac{-40}{48}=\dfrac{-22}{48}=\dfrac{-11}{24}\)
\(d,\dfrac{-3}{4}+\dfrac{2}{5}=\dfrac{-15}{20}+\dfrac{8}{20}=\dfrac{-7}{20}\)
\(e,\dfrac{1}{6}+\dfrac{-3}{2}=\dfrac{2}{12}+\dfrac{-18}{12}=\dfrac{16}{12}=\dfrac{4}{3}\)
\(f,\dfrac{-2}{5}+\dfrac{-4}{3}=\dfrac{-6}{15}+\dfrac{-20}{15}=\dfrac{-26}{15}\)
\(g,\dfrac{1}{8}+\dfrac{-3}{4}=\dfrac{4}{32}+\dfrac{-24}{32}=\dfrac{20}{32}=\dfrac{5}{8}\)
\(h,\dfrac{-3}{4}+\dfrac{3}{7}=\dfrac{-21}{28}+\dfrac{12}{28}=\dfrac{-9}{28}\)
\(i,\dfrac{-3}{4}+\dfrac{-4}{5}=\dfrac{-15}{20}+\dfrac{-16}{20}=\dfrac{-31}{20}\)
\(k,\dfrac{-5}{25}+\dfrac{-7}{14}=\dfrac{-70}{350}+\dfrac{-175}{350}=\dfrac{-245}{350}=\dfrac{-7}{10}\)
\(l,\dfrac{6}{21}+\dfrac{-3}{15}=\dfrac{90}{315}+\dfrac{-63}{315}=\dfrac{27}{315}=\dfrac{3}{35}\)
\(m,\dfrac{3}{4}-\dfrac{5}{8}+\dfrac{1}{2}=\dfrac{24}{32}-\dfrac{20}{32}+\dfrac{1}{2}=\dfrac{4}{32}+\dfrac{1}{2}=\dfrac{1}{8}+\dfrac{1}{2}=\dfrac{2}{16}+\dfrac{8}{16}=\dfrac{10}{16}=\dfrac{5}{8}\)
\(n,\dfrac{-3}{12}-\dfrac{1}{-4}+\dfrac{-2}{6}=\dfrac{-1}{4}-\dfrac{1}{-4}+\dfrac{-1}{3}=0+\dfrac{-1}{3}=\dfrac{-1}{3}\)
\(p,\dfrac{1}{3}+\dfrac{-3}{4}-\dfrac{5}{12}=\dfrac{4}{12}+\dfrac{-9}{12}-\dfrac{5}{12}=\dfrac{-5}{12}-\dfrac{5}{12}=\dfrac{-10}{12}=\dfrac{-5}{6}\)
Bài 2:
\(a,\dfrac{3}{5}+x=\dfrac{5}{6}\)
\(x=\dfrac{5}{6}-\dfrac{3}{5}\)
\(x=\dfrac{7}{30}\)
\(b,x-\dfrac{1}{4}=\dfrac{-5}{8}\)
\(x=\dfrac{-5}{8}+\dfrac{1}{4}\)
\(x=\dfrac{-3}{8}\)
\(c,x-\dfrac{2}{3}=\dfrac{7}{12}\)
\(x=\dfrac{7}{12}+\dfrac{2}{3}\)
\(x=\dfrac{5}{4}\)
\(d,x+\dfrac{-7}{15}=-1\dfrac{1}{20}\)
\(x=-1\dfrac{1}{20}-\dfrac{-7}{15}\)
\(x=\dfrac{-7}{12}\)
\(e,x-\dfrac{1}{2}=\dfrac{-3}{4}\)
\(x=\dfrac{-3}{4}+\dfrac{1}{2}\)
\(x=\dfrac{-1}{4}\)
\(f,x-\dfrac{3}{4}=\dfrac{1}{2}\)
\(x=\dfrac{1}{2}+\dfrac{3}{4}\)
\(x=\dfrac{5}{4}\)
\(g,x-\dfrac{1}{4}=\dfrac{5}{8}\cdot\dfrac{2}{3}\)
\(x-\dfrac{1}{4}=\dfrac{5}{12}\)
\(x=\dfrac{5}{12}+\dfrac{1}{4}\)
\(x=\dfrac{2}{3}\)
\(h,\dfrac{4}{5}-x=\dfrac{-8}{35}\)
\(x=\dfrac{4}{5}-\dfrac{-8}{35}\)
\(x=\dfrac{36}{35}\)
#YVA
1. a) 6² : 4 . 3 + 2 . 5²
= 36 : 4 . 3 + 2 . 25
= 9 . 3 + 50
= 27 + 50
= 77
b) 5 . 4² - 32 : 4²
= 5 . 16 - 32 : 16
= 80 - 2
= 78
c) 80 - (4 . 5² - 3 .2³)
= 80 - (4 . 25 - 3 . 8)
= 80 - (100 - 24)
= 80 - 76
= 4
d) 2448 : [119 - (23 - 6)]
= 2448 : (119 - 17)
= 2448 : 102
= 24
e) 23 . 85 + 15 . 23 + 170
= 23 . (85 + 15) + 170
= 23 . 100 + 170
= 2300 + 170
= 2470
f) 3³ . 2 - 5 . 2023⁰ + 36 : 3²
= 27 . 2 - 5 . 1 + 36 : 9
= 54 - 5 + 4
= 53
2. a) 123 - 5.(x + 4) = 38
5.(x + 4) = 123 - 38
5.(x + 4) = 85
x + 4 = 85 : 5
x + 4 = 17
x = 17 - 4
x = 13
b) (3.x - 2⁴) . 7³ = 2 . 7⁴
3x - 16 = 2 . 7⁴ : 7³
3x - 16 = 2 . 7
3x = 14 + 16
3x = 30
x = 30 : 3
x = 10
c) (2600 + 6400) - 3.x = 1200
9000 - 3x = 1200
3x = 9000 - 1200
3x = 7800
x = 7800 : 3
x = 2600
d) [(6.x - 72) : 2 - 84] . 28 = 5628
(6x - 72) : 2 - 84 = 5628 : 28
(6x - 72) : 2 - 84 = 201
(6x - 72) : 2 = 201 + 84
(6x - 72) : 2 = 285
6x - 72 = 285 . 2
6x - 72 = 570
6x = 570 + 72
6x = 642
x = 642 : 6
x = 107
e) 70 - 5(x - 3) = 45
5(x - 3) = 70 - 45
5(x - 3) = 25
x - 3 = 25 : 5
x - 3 = 5
x = 5 + 3
x = 8
f) 10 + 2.x = 4⁷ : 4⁵
10 + 2x = 4²
10 + 2x = 16
2x = 16 - 10
2x = 6
x = 6 : 2
x = 3
g) 2.x - 138 = 2³.2²
2x - 138 = 2⁵
2x - 138 = 32
2x = 32 + 138
2x = 170
x = 170 : 2
x = 85
h) 231 - (x - 6) = 1339 : 13
231 - (x - 6) = 103
x - 6 = 231 - 103
x - 6 = 128
x = 128 + 6
x = 134
`@` `\text {Ans}`
`\downarrow`
`j)`
\(x^{17}\div x^{12}=x^{17-12}=x^5\)
`k)`
\(x^8\div x^5=x^{8-5}=x^3\)
`r)`
\(a^5\div a^5=a^{5-5}=a^0=1\)
`l)`
\(x^4\div x=x^{4-1}=x^3\)
`m)`
\(x^7\div x^6=x^{7-6}=x\)
`n)`
\(x^9\div x^9=x^{9-9}=x^0=1\)
`o)`
\(a^{12}\div a^5=a^{12-5}=a^7\)
`p)`
\(a^8\div a^6=a^{8-6}=a^2\)
`q)`
\(a^{10}\div a^7=a^{10-7}=a^3\)
`r(2),`
\(1024\div4=2^{10}\div2^2=2^8\)
`t)`
\(512\div2^3=2^9\div2^3=2^6\)
Ta có \(\dfrac{1}{1.3}\)+\(\dfrac{1}{3.5}\)+\(\dfrac{1}{5.7}\)+...+\(\dfrac{1}{49.51}\)
=\(\dfrac{2}{2}\).(\(\dfrac{1}{1.3}\)+\(\dfrac{1}{3.5}\)+\(\dfrac{1}{5.7}\)+...+\(\dfrac{1}{49.51}\))
=\(\dfrac{1}{2}\).(\(\dfrac{2}{1.3}\)+\(\dfrac{2}{3.5}\)+\(\dfrac{2}{5.7}\)+...+\(\dfrac{2}{49.50}\))
=\(\dfrac{1}{2}\).(1-\(\dfrac{1}{3}\)+\(\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{7}+...+\dfrac{1}{49}-\dfrac{1}{51}\))
=\(\dfrac{1}{2}\).(\(1-\dfrac{1}{51}\))
=\(\dfrac{1}{2}\).\(\dfrac{50}{51}\)
=\(\dfrac{25}{51}\)
Ta có: \(\dfrac{1}{1\cdot3}+\dfrac{1}{3\cdot5}+...+\dfrac{1}{49\cdot51}\)
\(=\dfrac{1}{2}\left(\dfrac{2}{1\cdot3}+\dfrac{2}{3\cdot5}+...+\dfrac{2}{49\cdot51}\right)\)
\(=\dfrac{1}{2}\left(1-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{5}+...+\dfrac{1}{49}-\dfrac{1}{51}\right)\)
\(=\dfrac{1}{2}\left(1-\dfrac{1}{51}\right)\)
\(=\dfrac{1}{2}\cdot\dfrac{50}{51}=\dfrac{25}{51}\)
File: undefined
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