Đây là một phép toán sai

a) a+38+(-42)+44

=a+38+[+(44-42)]

= a+38+2

= a+40

b) -(-85)-(40-a)+135

= 85-(40-a)+135

=(85+40)-135-a

=135-135-a

=0-a

k cho mình nha!

a) a+38+(-42)+44

=a+38-42+44

=a+44-42+38

=a+40

b) -(-85)-(40-a)+135

=85-40-a+135

=35-a+135

=35+135-a

=170-a

ờ hay đấy

a: 785+135-85+65

=785-85+135+65

=700+200

=900

b: \(32\cdot39+52\cdot21-12\cdot39+21\cdot48\)

\(=39\cdot32-12\cdot39+52\cdot21+21\cdot48\)

\(=39\left(32-12\right)+21\left(52+48\right)\)

\(=39\cdot20+21\cdot100=2100+780=2880\)

c: \(5^4\cdot5^8:5^9\cdot6\cdot8\cdot7\)

\(=\dfrac{5^{12}}{5^9}\cdot48\cdot7\)

\(=125\cdot48\cdot7=42000\)

d: \(2021^0-\left\{15^2:\left[175+\left(2^3\cdot5^2-6\cdot25\right)\right]\right\}\)

\(=1-\dfrac{225}{175+8\cdot25-150}\)

\(=1-\dfrac{225}{25+220}\)

=1-1

=0

a) 785 + 135 - 85 + 65 = 900

b) 32.39 + 52.21 - 12.39 + 21.48 = 93.69

c) 5 mũ 4.5 mũ  8 ÷ 5 mũ 9.6 ÷ 8.7 = 0.134

d) 2021 mũ 0 - { 15 mũ 2 : [ 175 + ( 2 mũ 3.5 mũ  2 - 6.25 ) ] } = 2021 mũ 0 - { 152 : [ 175 + 17.27 ] } = 20210 - { 152 : 192.27 } = 20210 - 0.791 = 20209.209

4×11/3×22=2×2×11/3×11×2

=2/3

2^4150/2^750=2^3400

a) \(\left(81+19\right)+35=135\)

b) \(\left(78+22\right)+\left(65+135\right)=100+200=300\)

c) \(\left(234+17716\right)+23=17950+23=17973\)

d) \(\left(99+1\right)+85=100+85=185\)

\(a,81+35+19=\left(81+19\right)+35=100+35=135\\ b,78+65+135+22=\left(78+22\right)+\left(65+135\right)=100+200=300\\ c,234+17716+23=\left(234+17716\right)+23=17950+23=17973\\ d,85+99+1=85+\left(99+1\right)=85+100=185\)

A) 81+ 19 +35

=100+35=135

B) 78+65+135+22

=78+22+65+135

100+200=300 

mấy câu cx làm tương tự

a = (81+19)+35

=100+35=135

b = (78+22)+(65+135)

=100+200=300

c = (234+17716)+23

=17950+23=17973

d = (99+1)+85

=100+85=185

a) 81 + 35 + 19 = (81 + 19) + 35 = 100 + 35 = 135

b) 78 + 65 + 135 + 22 = (78 + 22) + (135 + 65) = 100 + 200 = 300

c) 234 + 17716 + 23 = 17950 + 23 = 17973

d) 85 + 99 + 1 = 85+ (99 + 1) = 85 + 100 = 185

\(a,=116+19=135\\ b,=143+135+22\\ =278+22=300\\ c,=17950+23=17973\\ d,=184+1=185\)

a) 90 – ( 30 – 20) = 90 – 10

                   = 80

90 – 30 – 20 = 60 - 20

                  = 40

b) 100 – (60 + 10) = 100 – 70

                   = 30

100 - 60 + 10 = 40 + 10

                   = 50

c) 135 – (30 + 5) = 135 – 35

                   = 100

135 – 30 – 5 = 105 – 5

                   = 100

d) 70 + (40 – 10) = 70 + 30

                   = 100

70 + 40 – 10 = 110 -10

                   = 100

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a) \(85^2+75^2+65^2+55^2-45^2-35^2-25^2-15^2\)

\(=\left(85^2-15^2\right)+\left(75^2-25^2\right)+\left(65^2-35^2\right)+\left(55^2-45^2\right)\)

\(=\left(85-15\right)\left(85+15\right)+\left(75-25\right)\left(75+25\right)+\left(65-35\right)\left(65+35\right)+\left(55-45\right)\left(55+45\right)\)

\(=70.100+50.100+30.100+10.100\)

\(=7000+5000+3000+1000\)

\(=16000\)

b) \(\frac{135^2+130.135+65^2}{135^2-65^2}\)

\(=\frac{135^2+2.60.135+65^2}{135^2-65^2}\)

\(=\frac{\left(135+65\right)^2}{\left(135-65\right)^2}\)

\(=\frac{200^2}{70^2}\) \(=\frac{200}{70}=\frac{20}{7}\)

Chọn C