\(\left(x+4\right)^2-81=0\Leftrightarrow\left(x+4\right)^2-9^2=0\)

\(\Leftrightarrow\left(x+4+9\right)\times\left(x+4-9\right)=0\)

\(\Leftrightarrow\left(x+13\right)\times\left(x-5\right)=0\)

\(\left[{}\begin{matrix}x+13=0\\x-5=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=-13\\x=5\end{matrix}\right.\)

<=> 3\(^{x-4}\)= 3\(^4\)

<=> x - 4 = 4

<=> x      = 4 + 4

<=> x      = 8

3^x-4  = 81

=> 3^x-4 = 3⁴

^=> x - 4 = 4

=> x= 4 + 4 =8

vậy x =8 . đúng 100% nha bạn. chọn mình nha.

a)(2x-1)2=81

x=20,75

b)x:(1/2)3=1/2

x=0,75

bn k cho mik nha!!!<3

a) x-2=(-6)+17

x-2 = 11

x =11+2

x= 13

Vậy...

b)x+2=(-9)-11

x+2 = -20

x= -20-2

x= -22

Vậy...

c) 2x+5=x-1

2x+5 -x = -1

x +5 = -1

x= -1-5

x= -6

Vậy...

a) \(B=\frac{\sqrt{x}-3}{x+\sqrt{x}+1}\left(ĐK:x\ge0\right)\)

\(=\frac{\sqrt{81}-3}{81+\sqrt{81}+1}=\frac{9-3}{81+9+1}=\frac{6}{91}\)

b) \(A=\frac{2x+1}{\sqrt{x^3}-1}-\frac{1}{\sqrt{x}-1}\left(ĐK:x\ge0;x\ne1\right)\)

\(=\frac{2x+1-x-\sqrt{x}-1}{\left(\sqrt{x}-1\right)\left(x+\sqrt{x}+1\right)}=\frac{x-\sqrt{x}}{\left(\sqrt{x}-1\right)\left(x+\sqrt{x}+1\right)}\)

\(=\frac{\sqrt{x}\left(\sqrt{x}-1\right)}{\left(\sqrt{x}-1\right)\left(x+\sqrt{x}+1\right)}=\frac{\sqrt{x}}{x+\sqrt{x}+1}\)

c) \(P=\frac{A}{B}\)

\(=\frac{\sqrt{x}}{x+\sqrt{x}+1}:\frac{\sqrt{x}-3}{x+\sqrt{x}+1}\left(ĐK:x\ge0;x\ne9\right)\)

\(=\frac{\sqrt{x}}{\sqrt{x}-3}\)

\(=\frac{\left(\sqrt{x}-3\right)+3}{\sqrt{x}-3}=1+\frac{3}{\sqrt{x}-3}\)

Vậy để P nguyên thì: \(\sqrt{x}-3\inƯ\left(3\right)\)

\(\Leftrightarrow\sqrt{x}-3\in\left\{-1;1;-3;3\right\}\)

+) \(\sqrt{x}-3=-1\Leftrightarrow\sqrt{x}=2\Leftrightarrow x=4\left(tm\right)\)

+) \(\sqrt{x}-3=1\Leftrightarrow\sqrt{x}=4\Leftrightarrow x=16\left(tm\right)\)

+) \(\sqrt{x}-3=-3\Leftrightarrow\sqrt{x}=0\Leftrightarrow x=0\left(tm\right)\)

+) \(\sqrt{x}-3=3\Leftrightarrow\sqrt{x}=6\Leftrightarrow x=36\left(tm\right)\)

Vậy...........

\(\left(2600+6400\right)-3\cdot x=2000\)

\(9000-3x=2000\)

\(3x=9000-2000\)

\(3x=7000\)

\(x=7000:3\)

\(x=\frac{7000}{3}\)