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76 + 6 = 82

homeworks bỏ s nha bạn, vì đó là danh từ không đếm được

⇒ homework

bài 20:

\(a.4^{n}=256\)

\(4^{n}=4^4\)

⇒ n = 4

b . \(9^{5n-8}=81\)

\(9^{5n-8}=9^2\)

⇒ 5n - 8 = 2

5n = 2 + 8

5n = 10

n = 10 : 5 = 2

c. \(3^{n+2}:27=3\)

\(3^{n+2}=3\cdot27\)

\(3^{n+2}=81\)

\(3^{n+2}=3^4\)

⇒ n + 2 = 4

⇒ n = 4 - 2 = 2

d. \(8^{n+2}\cdot2^3=8^5\)

\(8^{n+2}=8^5:2^3\)

\(8^{n+2}=8^4\)

⇒ n + 2 = 4

⇒ n = 4 - 2 = 2

bài 21 :

\(a.30-2x^2=12\)

\(2x^2=30-12\)

\(2x^2=18\)

\(x^2=18:2\)

\(x^2=9\)

⇒ x = 3 hoặc x = -3

b. \(\left(9-2x\right)^3=125\)

\(\left(9-2x\right)^3=5^3\)

⇒ 9 - 2x = 5

2x = 9 - 5

2x = 4

x = 4 : 2 = 2

c. \(\left(2x-2\right)^4=0\)

⇒ 2x - 2 = 0

2x = 2

x = 2 : 2 = 1

d. \(\left(x+5\right)^3=\left(2x\right)^3\)

⇒ x + 5 = 2x

⇒ 2x - x = 5

x = 5

\(a.16=\left(x-5\right)^2\)

\(\Rightarrow\left[\begin{array}{l}x-5=4\Rightarrow x=9\\ x-5=-4\Rightarrow x=1\end{array}\right.\)

vậy x thuộc {9; 1}

b. \(\left(x-1\right)^3-27=0\)

\(\Rightarrow\left(x-1\right)^3=27\)

\(\left(x-1\right)^3=3^3\)

⇒ x - 1 = 3

⇒ x = 3 + 1 = 4

c. \(\left(7x-11\right)^3-2^5\cdot5^2=200\)

\(\left(7x-11\right)^3-800=200\)

\(\left(7x-11\right)^3=200+800\)

\(\left(7x-11\right)^3=1000\)

\(\left(7x-11\right)^3=10^3\)

⇒ 7x - 11 = 10

7x = 10 + 11

7x = 21

x = 21 : 7 = 3

d. \(x^2=x^5\)

\(\Rightarrow x^5-x^2=0\)

\(x^2\cdot\left(x^3-1\right)=0\)

\(x^2\cdot\left(x-1\right)\cdot\left(x^2+x+1\right)=0\)

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

vậy x thuộc {0; 1}

e. \(\left(3x-1\right)^{10}=\left(3x-1\right)^{20}\)

\(\Rightarrow\left(3x-1\right)^{10}\cdot\left\lbrack1-\left(3x-1\right)^{10}\right\rbrack=0\)

\(\Rightarrow\left[\begin{array}{l}\left(3x-1\right)^{10}=0\Rightarrow x=\frac13\\ \left(3x-1\right)^{10}=1\end{array}\right.\Rightarrow\left[\begin{array}{l}x=\frac13\\ \left[\begin{array}{l}3x-1=1\Rightarrow x=\frac23\\ 3x-1=-1\Rightarrow x=0\end{array}\right.\end{array}\right.\)

vậy \(x\in\left\lbrace\frac13;\frac23;0\right\rbrace\)

không được nha bạn

\(\frac{9,6\times2,5+4,8\times3,5\times2+19,2\times2}{5,6\times14,5-6,5\times0,8-4,5\times5,6-3,5\times0,8}\)

\(=\frac{9,6\times2,5+9,6\times3,5+19,2\times2}{5,6\times\left(14,5-4,5\right)-0,8\times\left(6,5+3,5\right)}\)

\(=\frac{9,6\times\left(2,5+3,5\right)+9,6\times2\times2}{5,6\times10-0,8\times10}\)

\(=\frac{9,6\times6+9,6\times4}{10\times\left(5,6-0,8\right)}\)

\(=\frac{9,6\times\left(6+4\right)}{10\times4,8}\)

\(=\frac{9,6\times10}{10\times4,8}\)

\(=\frac{9,6}{4,8}=\frac{96}{48}=2\)