Question

Baif2: Tìm x
a. 3 mũ 2 . x + 2 mũ 3 . x =51
b. 6 mũ 2 . 2 - (84 - 3 mũ 2 . x): 7 = 69
c. (x + 1) mũ 2= 64
e. (x - 1) mũ 2 = (x - 1) mũ 3
d. (2x + 1) mũ 3 = 27
g. 3 mũ x +2 =81

Answer 1

a) \(3^2.x+2^3.x=51\)

\(\Leftrightarrow x\left(3^2+2^3\right)=51\)

\(\Leftrightarrow17x=51\)

\(\Leftrightarrow x=3\)

Vậy

Answer 2

b) \(6^2.2-\left(84-3^2.x\right):7=69\)

\(\Leftrightarrow\left(84-3^2.x\right):7=3\)

\(\Leftrightarrow84-3^2.x=21\)

\(\Leftrightarrow3^2.x=63\)

\(\Leftrightarrow x=7\)

Vậy

Answer 3

c) \(\left(x+1\right)^2=64\)

\(\Leftrightarrow\orbr{\begin{cases}x+1=8\\x+1=-8\end{cases}\Leftrightarrow\orbr{\begin{cases}x=7\\x=-9\end{cases}}}\)

Vậy

Answer 4

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

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

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

\(\Leftrightarrow\orbr{\begin{cases}\left(x-1\right)^2=0\\x-1-1=0\end{cases}\Leftrightarrow\orbr{\begin{cases}x=1\\x=2\end{cases}}}\)

Vậy

Answer 5

d) \(\left(2x+1\right)^3=27\)

\(\Leftrightarrow2x+1=3\)

\(\Leftrightarrow x=1\)

Vậy

Answer 6

g) \(3^x+2=81\)

\(\Leftrightarrow3^x=79\)

ko có giá trị x nào thỏa mãn

Answer 7

a) \(3^2x+2^3x=51\)

\(\Leftrightarrow9x+8x=51\)

\(\Leftrightarrow17x=51\Leftrightarrow x=\frac{51}{17}=3\)

Vậy:....

Answer 8

b) \(6^2\cdot2-\left(84-3^2x\right):7=69\)

\(\Leftrightarrow36\cdot2-\left(84-9x\right):7=69\)

\(\Leftrightarrow72-\frac{84-9x}{7}=69\)

\(\Leftrightarrow\frac{504}{7}-\frac{84-9x}{7}=69\)

\(\Leftrightarrow\frac{504-84+9x}{7}=69\)

\(\Leftrightarrow\frac{420+9x}{7}=69\)

\(\Leftrightarrow420+9x=483\)

\(\Leftrightarrow9x=63\Leftrightarrow x=7\)

Vậy:....

Answer 9

c) \(\left(x+1\right)^2=64\)

\(\Leftrightarrow\left(x+1\right)^2=8^2\)

\(\Leftrightarrow x+1=8\)

\(\Leftrightarrow x=7\)

Vậy:...