GIÚP MÌNH VỚI

\(a,\left(2\times x-40\right):10=-55\)

\(2\times x-40=-55\times10\)

\(2\times x-40=-550\)

\(2\times x=-550+40\)

\(2\times x=-510\)

\(x=-510:2\)

\(\Rightarrow x=-255\)

\(b,\left(2\times x+15\right):5=-40\)

\(2\times x+15=-40\times5\)

\(2\times x+15=-200\)

\(2\times x=-200-15\)

\(2\times x=-215\)

\(x=-215:2\)

\(\Rightarrow x=-\dfrac{215}{2}\)

\(c,\left(2\times x-72\right):8=25\)

\(2\times x-72=25\times8\)

\(2\times x-72=200\)

\(2\times x=200+72\)

\(2\times x=272\)

\(x=272:2\)

\(\Rightarrow x=136\)

\(72^{45}-72^{44}=72^{44}.\left(72-1\right)=72^{44}.71\)

\(72^{44}-72^{43}=72^{43}.\left(72-1\right)=72^{43}.71\)

Vì \(72^{44}>72^{43}\Rightarrow72^{45}-72^{44}>72^{44}-72^{43}\)

x + 2 ∈ B(8) = {0; 8; 16; 24; 32; 40; 48; 56; 64; 72; 80; ...}

⇒ x ∈ {-2; 6; 14; 22; 30; 38; 46; 54; 62; 70; 78; ...}

Mà 18 ≤ x ≤ 72

⇒ x ∈ {22; 30; 38; 46; 54; 62; 70}

bài 1 : 

-72.(15-49)+15.(-56+72)

= -72.(-34) + 15.16

= 2448 + 240

= 2688

bài 2 : 

-2x-8=-72

=> -2x = -72 + 8

=> -2x = -64

=> x = -64 : (-2)

=> x = 32 thuộc Z

vậy____

Bài 1:

-72 . ( 15 - 49 ) + 15 . ( -56 + 72 )

= -72 . ( -34 ) + 15 . 16

= 2448 + 240

= 2688

Bài 2:

-2x - 8 = -72

-2x = -72 + 8

-2x = -64

   x = ( -64 ) : ( -2 )

   x = 32

Câu 3: 

\(2S=2+2^2+2^3+...+2^{10}\)

nên \(S=2^{10}-1\)

\(5\cdot2^8=256\cdot5=1280>1023=2^{10}-1\)

Do đó: \(S< 5\cdot2^8\)

-2(2.x-8)+3(4-2.x)=-72-5(3.x-7)

<=>16-4x+12-6x =-72-15x+35

<=>16-4x+12-6x+72+15x-35=0

<=>65+5x=0

<=>x=-13

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Chọn A

a) [( 6.x-72):2-84].28(thiếu đề)

b) (19.x + 2.5²) :14= (13-8)2 - 4

(19.x + 2.25) :14= 5.2 - 4

(19.x + 50) :14=10- 4

(19.x + 50) :14=6

19.x + 50=6.14

19.x +50=84

19.x=84-50

19.x=34

x=34:19

x=34/19