Bài 4:

a: =>7/x-5=2

=>x-5=7/2

=>x=17/2

b: =>1-2x=-5

=>2x=6

=>x=3

c: =>2x-3=5 hoặc 2x-3=-5

=>2x=8 hoặc 2x=-2

=>x=-1 hoặc x=4

d: =>2(x+1)^2+17=21

=>2(x+1)^2=4

=>(x+1)^2=2

=>\(x+1=\pm\sqrt{2}\)

=>\(x=\pm\sqrt{2}-1\)

40% x X + 20% = 72

=>2/5 x X +1/5 =72

2/5 x X = 72 - 1/5

2/5 x X = 359/5

X=359/2

X=179,5

40%xX+20%=72

=> \(\frac{2}{5}xX+\frac{1}{5}=72\)

=> \(\frac{2}{5}xX=72-\frac{1}{5}=\frac{359}{5}\)

=> \(X=\frac{359}{5}:\frac{2}{5}=\frac{359}{2}\)

tích nha !

x=120

x×(40%+20%)=72

x×0,6=72

x=72:0,6

x=120

40% x X+X x 20%=72

X x (40%+20%)=72

X x 60% =72

X = 72 : 60%

X=120\

Học tốt

\(40\%\times x+x\times20\%=72\)

\(\left(40\%+20\%\right)\times x=72\)

                     \(60\%\times x=72\)

                                    \(x=72:60\%\)

                                    \(x=120\)

b) 54,3 x 4,7 + 54,3 x 4,3 + 54,3

= 54,3 x (4,7 + 4,3 + 1)

= 54,3 x 10

= 543

\(2^x-26=6\\ \Leftrightarrow2^x=32\\ \Leftrightarrow2^x=2^5\\ \Leftrightarrow x=5\)

\(2^x-26=6\)

⇒ \(2^x=6+26=32\)

⇒ \(2^x=32=2^5\)

⇒ \(x=5\)

\(2^x-26=6\)

\(2^x=6+26=32\)

\(2^x=2^5\)

=> x = 5

Vậy x = 5

a,100%X-40%X=3,6

=>60%X=3,6

=>X=3,6:60%

=>X=6

b,30%X+100%=52

=>130%X=52

=>X=52:130%

=>X=40

\(\sqrt{x+1}+\sqrt{4x+4}=6\)

\(\Leftrightarrow\sqrt{x+1}+4\sqrt{x+1}=6\)

\(\Leftrightarrow5\sqrt{x+1}=6\)

\(\Leftrightarrow\sqrt{x+1}=\dfrac{6}{5}\)

\(\Leftrightarrow x+1=\left(\dfrac{6}{5}\right)^2\)

\(\Leftrightarrow x+1=\dfrac{36}{25}\)

`<=> x= 11/25`

** Bổ sung điều kiện $x,y$ là các số nguyên. 

$x+5y+xy=6$

$(x+xy)+5y=6$

$x(1+y)+5(y+1)=11$

$(y+1)(x+5)=11$
Vì $x,y$ nguyên nên $x+5, y+1$ cũng nguyên. Ta xét các TH sau:

TH1: $x+5=1, y+1=11\Rightarrow x=-4; y=10$
TH2: $x+5=11, y+1=1\Rightarrow x=6; y=0$

TH3: $x+5=-1; y+1=-11\Rightarrow x=-6; y=-12$

TH4: $x+5=-11; y+1=-1\Rightarrow x=-16; y=-2$

Vì 1⁵= 1⁶ nên x - 5 = 1

x= 1+5

x=6

\(\left(x-5\right)^5=\left(x-5\right)^6\)

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

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

\(\Rightarrow\left[{}\begin{matrix}x=5\\x=6\end{matrix}\right.\)

\(\left(x-5\right)^5=\left(x-5\right)^6\)

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

\(\Rightarrow\left(x-5\right)^5.\left(x-5-1\right)=0\)

\(\Rightarrow\left(x-5\right)^5.\left(x-6\right)=0\)

\(\Rightarrow\left\{{}\begin{matrix}\left(x-5\right)^5=0\\x-6=0\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=5\\x=6\end{matrix}\right.\)