lớp mấy vậy bạn

40 - - là s z 

c) C = 5 + 5² + 5³ +...+ 5⁸

       = ( 5 + 5² ) + ( 5³ + 5⁴ ) + ( 5⁵ + 5⁶ ) + ( 5⁷ + 5⁸ )

       = 5 + 5² + 5²( 5 + 5² ) + 5⁴( 5 + 5² ) + 5⁶( 5 + 5² )

       = 5 + 5² ( 1 + 5² + 5⁴ + 5⁶ )

       = 30. ( 1 + 5² + 5⁴ + 5⁶ ) chia hết cho 30

Vậy C = 5 + 5² + 5³ +...+ 5⁸ chia hết cho 30

b) B = 16⁵ + 2¹⁵

        = (2⁴)⁵ + 2¹⁵

        = 2²⁰ + 2¹⁵

        = 2¹⁵. 2⁵ + 2¹⁵

        = 2¹⁵(2⁵ + 1)

        = 2¹⁵.33 chia hết cho 33

Vậy B = 16⁵ + 2¹⁵ chia hết cho 33

B

B

a) \(A=\left\{1;2;3;4;5\right\}\)

\(\Rightarrow A=\left\{x\inℕ|1\le x\le5\right\}\)

b) \(B=\left\{0;1;2;3;4\right\}\)

\(\Rightarrow B=\left\{x\inℕ|0\le x\le4\right\}\)

c) \(C=\left\{1;2;3;4\right\}\)

\(\Rightarrow C=\left\{x\inℕ|1\le x\le4\right\}\)

d) \(D=\left\{0;2;4;6;8\right\}\)

\(\Rightarrow D=\left\{x\inℕ|x=2k;0\le k\le4;k\inℕ\right\}\)

e) \(E=\left\{1;3;5;7;9;...49\right\}\)

\(\Rightarrow E=\left\{x\inℕ|x=2k+1;0\le k\le24;k\inℕ\right\}\)

f) \(F=\left\{11;22;33;44;...99\right\}\)

\(\Rightarrow F=\left\{x\inℕ|x=11k;1\le k\le9;k\inℕ\right\}\)

Bngxgyfiyfyg

Bài 1: 

a) Ta có: \(x\left(x^2-4\right)=0\)

\(\Leftrightarrow x\left(x-2\right)\left(x+2\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x=0\\x-2=0\\x+2=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=0\\x=2\\x=-2\end{matrix}\right.\)

Vậy: \(x\in\left\{0;2;-2\right\}\)

b) Ta có: \(\left(2x-3\right)+\left(-3x\right)-\left(x-5\right)=40\)

\(\Leftrightarrow2x-3-3x-x+5=40\)

\(\Leftrightarrow-2x+2=40\)

\(\Leftrightarrow-2x=38\)

hay x=-19

Vậy: x=-19

Bài 2: 

a) Ta có: \(-45\cdot12+34\cdot\left(-45\right)-45\cdot54\)

\(=-45\cdot\left(12+34+54\right)\)

\(=-45\cdot100\)

\(=-4500\)

b) Ta có: \(43\cdot\left(57-33\right)+33\cdot\left(43-57\right)\)

\(=43\cdot57-43\cdot33+43\cdot33-33\cdot57\)

\(=43\cdot57-33\cdot57\)

\(=57\cdot\left(43-33\right)\)

\(=57\cdot10=570\)

 a)\(...A=\dfrac{2^{50+1}-1}{2-1}=2^{51}-1\)

b) \(...\Rightarrow B=\dfrac{3^{80+1}-1}{3-1}=\dfrac{3^{81}-1}{2}\)

c) \(...\Rightarrow C+1=1+4+4^2+4^3+...+4^{49}\)

\(\Rightarrow C+1=\dfrac{4^{49+1}-1}{4-1}=\dfrac{4^{50}-1}{3}\)

\(\Rightarrow C=\dfrac{4^{50}-1}{3}-1=\dfrac{4^{50}-4}{3}=\dfrac{4\left(4^{49}-1\right)}{3}\)

Tương tự câu d,e,f bạn tự làm nhé

Từ a và b bạn tích ra các số còn lai rồi nhân lại bằng máy tính là được mà bạn^^

a, 28 . (-2).3 - { 136 + [54 - 28 : (69 - 71).2 ]}

=-168- { 136 + [54 - 28 : (-2).2 ]}

=-168 - [136 + (54+28)]

=-168 - 218

=-386

b) 203.46-203.37+203

=203.46-203.37+203.1

=203.(46-37+1)

=203.10

=2030

c)21+23+25+27+29-31-33-35-37-39

=(21-31)+(23-33)+(25-35)+(27-37)+(29-39)

= -10 + (-10) + (-10) + (-10) + (-10)

=-50

d) 18.17-3.6.17

=18.17-18.17

= 0

e,33. ( 107- 112) - 107 . ( 33- 112)

=33.107- 33.112- 107.33+107.112

=(33.107- 33.112- 107.33)+107.112

=33(107-112-107)+107.112

=-33.112+107.112

=112.(-33+107)

=112.74

=8288

vậy à

1-b ; 2-e ; 3-d ; 4-a ; 5- c