\(=120+\left(55-5^2\right)+8=128+\left(55-25\right)=128+30=158\)

Mở máy. Bấm tổ hợp phím:

a) 2 ( 3 x 5 \(x^2\) - 2 ( 5 + 7 ) ) +3 \(x^{[]}\) 3 =

Kết quả:129

b) 3 ( 120 + ( 55 - ( 11 - 3 x 2 ) \(x^2\) ) ) +2 \(x^{[]}\) 3 =

Kết quả: 458

b: =-329+115-101-15+440=100+10=110

120+[55-(11-3.2)²]+1²⁰²¹
= 120+(55-25)+1
= 120+30-1
= 149
-329+(115-101)-(15-440)
= -329+14+425
= 100

Câu 2:

\(a,\Rightarrow x=-23+15=-8\\ b,\Rightarrow5\left(x+4\right)=85\\ \Rightarrow x+4=17\Rightarrow x=13\\ c,\Rightarrow5^{x+2}=24+1=25=5^2\\ \Rightarrow x+2=2\Rightarrow x=0\\ d,\Rightarrow x+4+x+5⋮9\\ \Rightarrow2x+9⋮9\\ \Rightarrow2x⋮9\Rightarrow x\in\left\{0;9\right\}\left(0< x< 10\right)\)

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rất đúng

1)

a) 2x + 5 = 3⁴ : 3²

2x + 5 = 3²

2x + 5 = 9

2x = 9 - 5

2x = 4

x = 4 : 2

x = 2

b) (3x - 24).73 = 2.74

(3x - 24).73 = 148

3x - 24 = 148/73

3x = 148/73 + 24

3x = 1900/73

x = 1900/73 : 3

x = 1900/219

c) [3.(42 - x)] + 15 = 23.3

126 - 3x + 15 = 69

141 - 3x = 69

3x = 141 - 69

3x = 72

x = 72 : 3

x = 24

d) 126 + (132 - x) = 300

132 - x = 300 - 126

132 - x = 174

x = 132 - 174

x = -42

2)

a) 120 - (x + 55) = 60

x + 55 = 120 - 60

x + 155 = 60

x = 60 - 55

x = 5

b) (7x - 11).3 = 25.52 + 200

(7x - 11).3 = 1500

7x - 11 = 1500 : 3

7x - 11 = 500

7x = 500 + 11

7x = 511

x = 511 : 7

x = 73

c) 2x + 2x + 4 = 544

4x = 544 - 4

4x = 540

x = 540 : 4

x = 135

\(a,=6x^2+23x+21-\left(6x^2+23x-55\right)\\ =76\left(đpcm\right)\\ b,=3x^4+6x^3+9x^2-2x^3-4x^2-6x+x^2+2x+3-4x^3+4x-3x^4-6x^2\\ =3\left(đpcm\right)\)

`@` `\text {Ans}`

`\downarrow`

Gửi c!

Bài 1: 

a) \(3x^2\left(2x^3-x+5\right)-6x^5-3x^3+10x^2\)

\(=6x^5-3x^3+10x^2-6x^5-3x^3+10x^2\)

\(=10x^2+10x^2\)

\(=20x^2\)

b) \(-2x\left(x^3-3x^2-x+11\right)-2x^4+3x^3+2x^2-22x\)

\(=-2x^4+6x^3+2x^2-22x-2x^4+3x^3+2x^2-22x\)

\(=-4x^4+9x^3+4x^2-44x\)

\(\dfrac{1}{55^2}.5^4.\left(-11\right)^2.55^5.\left(\dfrac{1}{5^2}\right)^2:\left(5^3.11^6\right)\)

\(=\dfrac{5^4.11^2.5^5.11^5}{5^2.11^2}.\dfrac{1}{5^4.5^3.11^6}\)

\(=\dfrac{5^9.11^7}{5^9.11^8}=\dfrac{1}{11}\)

\(=\dfrac{1}{5^2\cdot11^2}\cdot5^4\cdot11^2\cdot55^5\cdot\left(\dfrac{1}{5}\right)^2\cdot\dfrac{1}{5^3\cdot11^6}\)

\(=5^2\cdot5^5\cdot11^5\cdot\dfrac{1}{5^2\cdot5^3\cdot11^6}\)

\(=\dfrac{11^5}{11^6}\cdot\dfrac{5^7}{5^5}=\dfrac{25}{11}\)

a) \(S4=\frac{3}{50}+\frac{3}{150}+\frac{3}{300}+...+\frac{3}{9500}\)

\(S4=\frac{3}{5.10}+\frac{3}{10.15}+\frac{3}{15.20}+...+\frac{3}{95.100}\)

\(S4=\frac{3}{5}\left(\frac{1}{5}-\frac{1}{10}+\frac{1}{10}-\frac{1}{15}+\frac{1}{15}-\frac{1}{20}+...+\frac{1}{95}-\frac{1}{100}\right)\)

\(S4=\frac{3}{5}\left(\frac{1}{5}-\frac{1}{100}\right)\)

\(S4=\frac{3}{5}.\frac{19}{100}\)

\(S4=\frac{57}{500}\Rightarrow S=\frac{57}{500}:4=\frac{57}{2000}\)

b) \(S5=\frac{55}{11.16}+\frac{55}{16.21}+...+\frac{55}{36.41}\)

\(S5=\frac{55}{5}.\left(\frac{1}{11}-\frac{1}{16}+\frac{1}{16}-\frac{1}{21}+...+\frac{1}{36}-\frac{1}{41}\right)\)

\(S5=11.\left(\frac{1}{11}-\frac{1}{41}\right)\)

\(S5=11.\frac{30}{451}\)

\(S5=\frac{30}{41}\Rightarrow S=\frac{30}{41}:5=\frac{6}{41}\)

Mình không hiểu ý bạn là S.4 hay là S4 là tên