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b, -418 - {- 418 - [ -418 - (-418) + 2021]}
= -481 - { -418 - [ 0 + 2021]}
= -481 + 418 + 2021
= 2021
d, 23 - 501 - 343 + 61 - 257 + 16 - 499
= (23 + 61 + 16) - (501 + 499) - (343 + 257)
= 100 - 1000 - 600
= 100 - 1600
= -1500
e, 743 - 231 + (-495) - (-69) - 38 + (-117)
= 512 - 426 - 155
= 86 - 155
= - 69
\(a,\left(2x-16\right)^7=128\\ \Rightarrow\left(2x-16\right)^7=2^7\\ \Rightarrow2x-16=2\\ \Rightarrow2x=18\\ \Rightarrow x=9\\ b,x^3.x^2=2^8:2^3\\ \Rightarrow x^5=2^5\\ \Rightarrow x=5\\ c,3^{x-3}-3^2=2.3^2\\ \Rightarrow3^{x-3}-9=18\\ \Rightarrow3^{x-3}=27\\ \Rightarrow3^{x-3}=3^3\\ \Rightarrow x-3=3\\ \Rightarrow x=6\)
a)A=(-123) - 77 + (-257) +23 - 43 b)B=48+| 48-174|+(-74)
A=[(-123) - 77]+[(-257)-43]+23 B=48+(174-48)+(-74)
A= -200+(-300)+23 B=48+174+(-48)+(-74)
A= -500+23 B=[48+(-48)]+[174+(-74)]
A= -477 B=0+100=100
c)C= -2012+(-596)+(-201)+496+301 d)D=1+2-3-4+5+6-7-8+............-79-80-81
C= -2012+[(-596)+496]+[(-201)+301] D=1+(2-3-4+5)+(6-7-8+9)+............+(78-79-80-81)
C= -2010+(-100)+100 D=1+0+0+............+(-162)
C= -2010+0 D=1+(-162)
C= -2010 D= -161
a, \(\dfrac{1}{2}\) - ( - \(\dfrac{1}{3}\) ) + \(\dfrac{1}{23}\) + \(\dfrac{1}{6}\)
= \(\dfrac{5}{6}\) + \(\dfrac{1}{23}\) + \(\dfrac{1}{6}\)
= 1 + \(\dfrac{1}{23}\)
= \(\dfrac{24}{23}\)
b, \(\dfrac{11}{24}\) - \(\dfrac{5}{41}\) + \(\dfrac{13}{24}\) + 0,5 - \(\dfrac{36}{41}\)
= (\(\dfrac{11}{24}\) + \(\dfrac{13}{24}\)) - ( \(\dfrac{5}{41}\) + \(\dfrac{36}{41}\)) + 0,5
= 1 - 1 + 0,5
= 0,5
c,\(-\dfrac{1}{12}-\left(\dfrac{1}{6}-\dfrac{1}{4}\right)\)
=\(-\dfrac{1}{12}-\left(-\dfrac{1}{12}\right)\)
=0
d, \(\dfrac{1}{6}-\left[\dfrac{1}{6}-\left(\dfrac{1}{4}+\dfrac{9}{12}\right)\right]\)
= \(\dfrac{1}{6}-\left[\dfrac{1}{6}-1\right]\)
= \(\dfrac{1}{6}-\left(-\dfrac{5}{6}\right)\)
= 1
a) 4x + 32 = 3 . 25
4x + 32 = 3 . 32 = 96
4x = 96 - 32 = 64
4x = 43
=> x = 3
b) 86 - 5( x + 8 ) = 616 : 614 ( Bài này mình bấm máy k ra :v Xem lại nhé )
c) 38 - 3 | x | = 5 ( 24 - 22 . 3 )
38 - 3 | x | = 5 ( 16 - 4 . 3 )
38 - 3 | x | = 5 . 4
38 - 3 | x | = 20
3 | x | = 38 - 20
3 | x | = 18
| x | = 18 : 3 = 6
=> x = 6 hoặc x = -6
d) 2018 < | x | < 2020
=> | x | = { 2019 ; 2020 }
=> x = { -2019 ; 2019 ; -2020 ; 2020 }
a) \(\dfrac{3}{8}+\dfrac{15}{-25}+\dfrac{3}{5}\)
\(=\dfrac{-9}{40}+\dfrac{3}{5}\)
\(=\dfrac{3}{8}\)
b) \(\dfrac{-5}{18}+\dfrac{23}{45}-\dfrac{9}{10}\)
\(=\dfrac{7}{30}-\dfrac{9}{10}\)
\(=\dfrac{-2}{3}\)
c) \(\dfrac{-5}{12}+\dfrac{15}{18}-2,25\)
\(=\dfrac{5}{12}-2,25\)
\(=\dfrac{-11}{6}\)
d) \(\dfrac{5}{6}+\dfrac{2}{3}-0,5\)
\(=\dfrac{3}{2}-0,5\)
\(=1\)
a) \(\dfrac{13}{20}+\dfrac{3}{5}+x=\dfrac{5}{6}\)
\(\Rightarrow\dfrac{5}{4}+x=\dfrac{5}{6}\)
\(\Rightarrow x=\dfrac{5}{6}-\dfrac{5}{4}\)
\(\Rightarrow x=\dfrac{-5}{12}\)
b) \(x+\dfrac{1}{3}=\dfrac{2}{5}-\dfrac{-1}{3}\)
\(\Rightarrow x+\dfrac{1}{3}=\dfrac{11}{15}\)
\(\Rightarrow x=\dfrac{11}{15}-\dfrac{1}{3}\)
\(\Rightarrow x=\dfrac{2}{5}\)
c)\(\dfrac{-5}{8}-x=\dfrac{-3}{20}-\dfrac{-1}{6}\)
\(\dfrac{-5}{8}-x=\dfrac{1}{60}\)
\(\Rightarrow x=\dfrac{-5}{8}-\dfrac{1}{60}\)
\(\Rightarrow x=\dfrac{-77}{120}\)
d) \(\dfrac{3}{5}-x=\dfrac{1}{4}+\dfrac{7}{10}\)
\(\Rightarrow\dfrac{3}{5}-x=\dfrac{19}{20}\)
\(\Rightarrow x=\dfrac{3}{5}-\dfrac{19}{20}\)
\(\Rightarrow x=\dfrac{-7}{20}\)
e) \(\dfrac{-3}{7}-x=\dfrac{4}{5}+\dfrac{-2}{3}\)
\(\Rightarrow\dfrac{-3}{7}-x=\dfrac{2}{15}\)
\(\Rightarrow x=\dfrac{-3}{7}-\dfrac{2}{15}\)
\(\Rightarrow x=\dfrac{-59}{105}\)
g) \(\dfrac{-5}{6}-x=\dfrac{7}{12}+\dfrac{-1}{3}\)
\(\Rightarrow\dfrac{-5}{6}-x=\dfrac{1}{4}\)
\(\Rightarrow x=\dfrac{-5}{6}-\dfrac{1}{4}\)
\(\Rightarrow x=\dfrac{-13}{12}\)
i don't now
mong thông cảm !
...........................
\(A=\frac{1}{2^2}+\frac{1}{3^2}+\frac{1}{4^2}+...+\frac{1}{100^2}\)
ta có :
\(\frac{1}{2^2}< \frac{1}{1\cdot2}\)
\(\frac{1}{3^2}< \frac{1}{2\cdot3}\)
\(\frac{1}{4^2}< \frac{1}{3\cdot4}\)
...
\(\frac{1}{100^2}< \frac{1}{99\cdot100}\)
nên \(A< \frac{1}{1\cdot2}+\frac{1}{2\cdot3}+\frac{1}{3\cdot4}+...+\frac{1}{99\cdot100}\)
\(\Rightarrow A< 1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{99}-\frac{1}{100}\)
\(\Rightarrow A< 1-\frac{1}{100}\)
\(\Rightarrow A< \frac{99}{100}< 1\)
\(\Rightarrow A< 1\left(đpcm\right)\)
nhiều qá lm sao nổi
a) \(\left(-1\right)\left[5^2-\left(4^3\right)\right]=\left(-1\right)\left(25-64\right)=\left(-1\right)\left(-39\right)=39\)
b) \(71.64-32.\left(-7\right)+32.11=142.32+32.7+32.11\)
\(=32.\left(142+7+11\right)=32.\left(142+18\right)=32.160=5120\)
c) \(666-\left(-422\right)-100-88=666+422-100-88\)
\(=\left(666+422\right)-\left(100+88\right)=1088-188=900\)
d) \(23-501-343+61-257+16-499\)
\(=\left(23+61+16\right)-\left(501+499\right)-\left(343+257\right)\)
\(=100-1000-600=100-\left(1000+600\right)=100-1600=-1500\)