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a ) 72 . 37 - 9 . 22 . 8 + 18 . 4 . 85
= 72 . 37 - 72 . 22 + 72 . 85
= 72 . ( 37 - 22 + 85 )
= 72 . 100
= 7200
b ) { 149 - [ 2 . ( 10 . 3 2 - 5 2 . 2 ) - 44 ] + 2 3 } : 11 2
= { 149 - [ 2 . 40 - 44 ] + 8 } : 121
= { 149 - 36 + 8 } : 121
= 121 : 121
= 1
a: \(61\cdot45+61\cdot23-68\cdot51\)
\(=61\left(45+23\right)-68\cdot51\)
\(=68\cdot61-68\cdot51\)
\(=68\left(61-51\right)=68\cdot10=680\)
b: \(3\cdot5^2-\left(75-4\cdot2^3\right)\)
\(=75-75+4\cdot8\)
\(=4\cdot8=32\)
c: \(36:\left\{2^2\cdot5-\left[30-\left(5-1\right)^2\right]\right\}\)
\(=\dfrac{36}{20-30+4^2}\)
\(=\dfrac{36}{-10+16}=\dfrac{36}{6}=6\)
d: \(\left(12\cdot49-3\cdot2^2\cdot7^2\right):\left(2020\cdot2021\right)\)
\(=\dfrac{\left(12\cdot49-12\cdot49\right)}{2020\cdot2021}=0\)
72^24-72^23=72^23(72-1)=71.72^23
72^23-72^22=72^22(72-1)=72^22.71
`- 9 . ( x - 6 ) + 20 = 56`
`=> -9 . ( x - 6 ) = 56-20`
`=> -9 . ( x - 6 ) =36`
`=>x-6=36:(-9)`
`=>x-6=-4`
`=>x=-4+6`
`=>x=2`
`-------------`
` ( 245 - x ) + 7^2=149`
`=>( 245 - x ) +49=149`
`=> 245 - x =149-49`
`=> 245 - x =100`
`=>x=245-100`
`=>x=145`
`------------`
`(2^x-3).7=35`
`=> 2^x-3=35:7`
`=> 2^x-3=5`
`=>2^x=5+3`
`=>2^x=8`
`=>2^x=2^3`
`=>x=3`
a) Ta có: 2711= (33)11=333
818=(34)8=332
Suy ra: 2711>818
Mình chỉ làm cho bn 1 ví dụ thôi. các bài còn lại bn làm tương tự nhé!
Sửa đề: \(S=\dfrac{1}{20}+\dfrac{1}{21}+\dfrac{1}{22}+...+\dfrac{1}{50}\)
Ta có: \(S=\dfrac{1}{20}+\dfrac{1}{21}+\dfrac{1}{22}+...+\dfrac{1}{50}\)
\(=\dfrac{1}{20}+\left(\dfrac{1}{21}+\dfrac{1}{22}+...+\dfrac{1}{30}\right)+\left(\dfrac{1}{31}+\dfrac{1}{32}+...+\dfrac{1}{40}\right)+\left(\dfrac{1}{41}+\dfrac{1}{42}+...+\dfrac{1}{50}\right)\)
\(\Leftrightarrow S>\dfrac{1}{20}+\dfrac{1}{3}+\dfrac{1}{4}+\dfrac{1}{5}=\dfrac{1}{4}+\dfrac{1}{3}+\dfrac{1}{4}\)
\(\Leftrightarrow S>\dfrac{1}{4}+\dfrac{1}{4}+\dfrac{1}{4}=\dfrac{3}{4}\)(đpcm)
a) (-12). (7 - 72) - 25. (55 - 43)
= (-12). (- 65) - 25. 12
= 12. 65 – 12. 25
= 12. (65 - 25)
= 12. 40
= 480
b) (39 - 19) : (- 2) + (34 - 22). 5
= 20 : (- 2) + 12. 5
= - 10 + 60
= 60 - 10
= 50.
325+172-72+65
= (325 + 65) + (172 - 72)
= 390 + 100
= 490
214+(-54)+(-14)+(-46)
= (214 - 14) - (54+46)
= 200 - 100
= 100
245-[(32-22).10-5]
= 245 - [(9 - 4). 10 - 5]
= 245 - [5.10 - 5]
= 245 - [50 - 5]
= 245 - 45
= 200
25.23-(9-14)+(29-34+20)
= 25. 8 + (29 - 9) - (34 - 20 - 14)
= 200 + 20 - 0
= 220
= 4 . 5 + (149 - 49)
= 20 + 100
= 120