`17/2 \div x=5`

`x=17/2 \div 5`

`x=17/10 = 1,7`

`----`

`x-3/8=2+1/4`

`x-3/8=9/4`

`x=9/4+3/8`

`x=21/8`

`\color{blue}\text {#DuyNam}`

\(\dfrac{17}{2}:x=5\)

\(x=\dfrac{17}{2}:5=\dfrac{17}{2}\times\dfrac{1}{5}\)

\(x=\dfrac{17}{10}\)

_____________________________

\(x-\dfrac{3}{8}=2+\dfrac{1}{4}\) \(=\dfrac{8}{4}+\dfrac{1}{4}\)

\(x-\dfrac{3}{8}=\dfrac{9}{4}\)

\(x=\dfrac{9}{4}+\dfrac{3}{8}=\dfrac{18}{8}+\dfrac{3}{8}\)

\(x=\dfrac{21}{8}\)

\(\dfrac{17}{9}-x=\dfrac{4}{3}\)

\(x=\dfrac{17}{9}-\dfrac{4}{3}\)

\(x=\dfrac{5}{9}\)

`17/9 - x = 5/7 : 15/28`

`=> 17/9 - x = 5/7 xx 28/15`

`=> 17/9 -x = 4/3`

`=> x = 17/9 - 4/3`

`=> x = 17/9 - 12/9`

`=> x = 15/9`

`=> x = 5/3`

Đặt A =  1.2 + 2.3 + 3.4 +.......... + 99.100

=> 3A = 1.2.3 + 2.3.(4 - 1) + 3.4.(5 - 2) + ..... + 99.100.(101 - 98)

=> 3A = 1.2.3 + 2.3.4 - 1.2.3 + 3.4.5 - 2.3.4 + ....... + 99.100.101 - 98.99.100

=> 3A = (1.2.3 + 2.3.4 + 3.4.5 + ....... + 99.100.101) - (1.2.3 + 2.3.4 + ......... + 98.99.100)

=> 3A = 99.100.101

=> A = 99.100.101 : 3 = 999900

2/11x13+2/13x15+2/15x17+....+2/95x97+2/97x99

=1/11-1/13+1/13-1/15+1/15-1/17+....+1/95-1/97+1/97-1/99

=1/11-1/99

=9/99-1/99

=8/99

đúng nhé bạn

a: \(280-\left(x-140\right):35=270\)

=>(x-140):35=280-270=10

=>x-140=350

=>x=350+140

=>x=490

b: \(\left(190-2x\right):35-32=16\)

=>\(\left(190-2x\right):35=32+16=48\)

=>\(190-2x=35\cdot48=1680\)

=>2x=190-1680=-1490

=>x=-745

c: \(720:\left\lbrack41-\left(2x-5\right)\right\rbrack=2^3\cdot5\)

=>\(720:\left\lbrack41-\left(2x-5\right)\right\rbrack=8\cdot5=40\)

=>41-(2x-5)=720:40=18

=>2x-5=41-18=23

=>2x=28

=>x=14

d: \(\left(x:23+45\right)\cdot37-22=2^4\cdot105\)

=>\(\left(\frac{x}{23}+45\right)\cdot37=16\cdot105+22=1702\)

=>\(\frac{x}{23}+45=46\)

=>\(\frac{x}{23}=1\)

=>x=23

e: \(\left(3x-4\right)\left(x-1\right)^3=0\)

=>\(\left[\begin{array}{l}3x-4=0\\ x-1=0\end{array}\right.\Rightarrow\left[\begin{array}{l}x=\frac43\\ x=1\end{array}\right.\)

f: \(2^{2x-1}:4=8^3\)

=>\(2^{2x-1-2}=2^9\)

=>2x-3=9

=>2x=12

=>x=6

g: \(x^{17}=x\)

=>\(x^{17}-x=0\)

=>\(x\left(x^{16}-1\right)=0\)

=>\(\left[\begin{array}{l}x=0\\ x^{16}-1=0\end{array}\right.\Rightarrow\left[\begin{array}{l}x=0\\ x^{16}=1\end{array}\right.\Rightarrow\left[\begin{array}{l}x=0\\ x=1\\ x=-1\end{array}\right.\)

h: \(\left(x-5\right)^4=\left(x-5\right)^6\)

=>\(\left(x-5\right)^6-\left(x-5\right)^4=0\)

=>\(\left(x-5\right)^4\cdot\left\lbrack\left(x-5\right)^2-1\right\rbrack=0\)

=>\(\left(x-5\right)^4\cdot\left(x-4\right)\left(x-6\right)=0\)

=>x∈{4;5;6}

i: \(\left(x+2\right)^5=2^{10}\)

=>\(\left(x+2\right)^5=\left(2^2\right)^5=4^5\)

=>x+2=4

=>x=2

k: 1+2+3+...+x=78

=>\(\frac{x\left(x+1\right)}{2}=78\)

=>x(x+1)=156

=>\(x^2+x-156=0\)

=>(x+13)(x-12)=0

=>x=-13(loại) hoặc x=12(nhận)

l: \(\left(3x-2^4\right)\cdot7^3=2\cdot7^4\)

=>\(3x-16=2\cdot\frac{7^4}{7^3}=2\cdot7=14\)

=>3x=16+14=30

=>\(x=\frac{30}{3}=10\)

n: \(5^{x}:5^2=125\)

=>\(5^{x-2}=5^3\)

=>x-2=3

=>x=5

m: \(\left(x+1\right)^2=\left(x+1\right)^0\)

=>\(\left(x+1\right)^2=1\)

=>\(\left[\begin{array}{l}x+1=1\\ x+1=-1\end{array}\right.\Rightarrow\left[\begin{array}{l}x=0\\ x=-2\end{array}\right.\)

o: Số số hạng của dãy số 2;4;..;52 là:

(52-2):2+1=50:2+1=25+1=26(số)

Tổng của dãy số 2;4;...;52 là:

\(\left(52+2\right)\cdot\frac{26}{2}=54\cdot13=702\)

(2+x)+(4+x)+...+(52+x)=780

=>26x+702=780

=>26x=78

=>x=3

p: \(70=2\cdot5\cdot7;80=2^4\cdot5\)

=>ƯCLN(70;80)=\(2\cdot5=10\)

70⋮x; 80⋮x

=>x∈ƯC(70;80)

=>x∈Ư(10)

mà x>8

nên x=10

q: \(12=2^2\cdot3;25=5^2;30=2\cdot3\cdot5\)

=>BCNN(12;25;30)=\(2^2\cdot3\cdot5^2=300\)

x⋮12; x⋮25; x⋮30

=>x∈BC(12;25;30)

=>x∈B(300)

mà 0<x<500

nên x=300

( X + 5,42 ) x 17 = 142,29

X + 5,42 = 142,29 : 17

X + 5,42 = 8,37

X = 8,37 - 5,42

X = 2,95

X x 8 + X x 15 = 653,2

X x ( 8 + 15 ) = 653,2

X x 23 = 653,2

X = 653,2 : 23

x = 28,4

( x + 5,42 ) x 17 = 142,29                             x . 8 + x . 15 = 653,2

  x + 5,42 = 142,29 : 17                                x . ( 8 + 15 ) = 653,2

  x + 5,42 = 8,37                                           x . 23 = 653,2

  x = 8,37 - 5,42                                            x = 653,2 : 23

  x = 2,95                                                      x = 28,4

máy tính ra :

1.5383844_x10¹¹

=153838440000

a

\(x^2\left(2x+15\right)+4\left(2x+15\right)=0\\ \Leftrightarrow\left(2x+15\right)\left(x^2+4\right)=0\\ \Leftrightarrow2x+15=0\left(x^2+4>0\forall x\right)\\ \Leftrightarrow2x=-15\\ \Leftrightarrow x=-\dfrac{15}{2}\)

b

\(5x\left(x-2\right)-3\left(x-2\right)=0\\ \Leftrightarrow\left(x-2\right)\left(5x-3\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}x-2=0\\5x-3=0\end{matrix}\right.\\ \Leftrightarrow\left[{}\begin{matrix}x=0+2=2\\x=\dfrac{0+3}{5}=\dfrac{3}{5}\end{matrix}\right.\)

c

\(2\left(x+3\right)-x^2-3x=0\\ \Leftrightarrow2\left(x+3\right)-\left(x^2+3x\right)=0\\ \Leftrightarrow2\left(x+3\right)-x\left(x+3\right)=0\\ \Leftrightarrow\left(x+3\right)\left(2-x\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}x+3=0\\2-x=0\end{matrix}\right.\\ \Leftrightarrow\left[{}\begin{matrix}x=0-3=-3\\x=2-0=2\end{matrix}\right.\)

a: =>(2x+15)(x^2+4)=0

=>2x+15=0

=>2x=-15

=>x=-15/2

b; =>(x-2)(5x-3)=0

=>x=2 hoặc x=3/5

c: =>(x+3)(2-x)=0

=>x=2 hoặc x=-3

a) x = 4

b) x = 5

c) x = 2

d) x = 2

e, x = 1

f, x = 0 hoặc  x = 1

a) x = 4                

b) x = 5     

c) x = 2                

d) x = 2

e) x = 1                

f) x = 0 hoặc  x = 1.