\(x^{20}=x\)

⇒\(x^{20}-x=0\)

⇒\(x\left(x^{19}-1\right)=0\)

⇔\(x^{19}-1=0\) hoặc x=0

⇔x=1 hoặc x=0

\(x^{20}=x\\ \Leftrightarrow x^{20}-x=0\\ \Leftrightarrow x\left(x^{19}-1\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}x=0\\x=1\end{matrix}\right.\)

\(x^{20}=x\\ \Rightarrow x\in\left\{0;1\right\}\)vì \(x\in N\)

\(\dfrac{x^2}{20}=\dfrac{4}{5}\)

\(\Leftrightarrow x^2=16\)

hay \(x\in\left\{4;-4\right\}\)

\(\dfrac{x}{3}=x+y=20\Rightarrow x=60\Rightarrow60+y=20\Rightarrow y=-40\)

Ta có:

\(\dfrac{x}{3}=20\)

\(\Rightarrow\)\(x=60\)

Lại có:

\(x+y=20\)

\(\Rightarrow\)\(y=20-60\)

\(\Rightarrow\)\(y=-40\)

Vây x = 60 và y = - 40

\(\dfrac{x}{3}=x+y\)

\(\Leftrightarrow x-\dfrac{1}{3}x=-y\)

\(\Leftrightarrow y=-\dfrac{2}{3}x\)

Ta có: x+y=20

\(\Leftrightarrow x\cdot\dfrac{1}{3}=20\)

hay x=60

=> y=40

X × 2,5 + 7,5 = 36,5

X × 2,5 = 36,5 - 7,5

X × 2,5 = 29

  X = 29 : 2,5

  X = 11,6

\(x\times2,5+7,5=36,5\\ x\times2,5=36,5-7,5\\ x\times2,5=29\\ x=29:2,5\\ x=11,6\)

\(x:15=\dfrac{1}{3}\)

\(x=5\)

\(x:15=\dfrac{1}{3}\Leftrightarrow x=5\)

\(x:15=\dfrac{8}{24}\)

\(\Rightarrow x:8=\dfrac{1}{3}\)

\(\Rightarrow x=\dfrac{1}{3}.15\)

\(\Rightarrow x=5\)

\(x+1538=3215\\ \Rightarrow x=3215-1538=1677\\ x-215=1578\\ \Rightarrow x=1578+215=1793\\ 345-x=182\\ \Rightarrow x=345-182=163\)

x+1538=3215⇒x=3215−1538=1677x−215=1578⇒x=1578+215=1793345−x=182⇒x=345−182=163

x+1538=3215⇒x=3215−1538=1677x−215=1578⇒x=1578+215=1793345−x=182⇒x=345−182=163

\(x=\dfrac{15}{13}+\dfrac{11}{13}=\dfrac{15+11}{13}=\dfrac{26}{13}\)

\(x=\dfrac{15}{13}+\dfrac{11}{13}\\ x=\dfrac{26}{13}\)

X = 11/13 + 15/13 = 26/13

\(x-\dfrac{1}{8}=\dfrac{4}{x-2}\) hay \(x-\dfrac{1}{8}=\dfrac{4}{x}-2\) vậy bạn?

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

=>\(\dfrac{\left(x-1\right)\left(x-2\right)}{8.\left(x-2\right)}=\dfrac{4.8}{\left(x-2\right).8}\)

=>khử mẫu

=>(x-1)(x-2)=32

.......

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

Bài 2: 

a: =>x-45=-20

hay x=25

b: =>35+30-5x=-12+112

=>65-5x=100

=>5x=-35

hay x=-7

c: =>x-124=1000

hay x=1124

d: \(\Leftrightarrow46-\left(3x-2\right)^3=-18\)

\(\Leftrightarrow\left(3x-2\right)^3=64\)

=>3x-2=4

hay x=2

Bài 2: 

a: =>x-45=-20

hay x=25

b: =>35+30-5x=-12+112=100

=>65-5x=100

=>5x=-35

hay x=-7

c: =>x-124=1000

hay x=1124

d: \(\Leftrightarrow46-\left(3x-2\right)^3=-18\)

\(\Leftrightarrow\left(3x-2\right)^3=64\)

=>3x-2=4

hay x=2