a,91-5(5+x)=61

=>25+5x=91-61=30

=>5x=30-25=5

=>x=1

b,\([\left(x+34\right)-50]\)x2=56

=>(x+34)-50=56:2=28

=>x+34=28+50=78

=>x=78-34=44.

c,1045-\([2015-\left(3x-24\right)]\)=5

=>2015-(3x-24)=1045-5=1040

=>3x-24=2015-1040=975

=>3x=975+24=999

=>x=999:3=333

d,\([195-\left(3x-27\right)]\)x39=4212

=>195-(3x-27)=4212:39=108

=>3x-27=195-108=87

=>3x=87+27=117

=>x=39

e,30-3(x-2)=18

=>30-3x+6=18

=>30-3x=18-6=12

=>3x=30-12=18

=>x=18:3=6

a) \(...\Rightarrow5\left(5+x\right)=91-61=30\)

\(\Rightarrow\left(5+x\right)=30:5=6\Rightarrow x=6-5=1\)

b) \(...\Rightarrow\left(x+34\right)-50=56:2=28\)

\(\Rightarrow\left(x+34\right)=28+50=78\Rightarrow x=78-34=44\)

c) \(...\Rightarrow2015-\left(3x-24\right)=1045-5=1040\)

\(\Rightarrow\left(3x-24\right)=2015-1040=975\)

\(\Rightarrow3x=975+24=999\Rightarrow x=999:3=333\)

d) \(...\Rightarrow195-\left(3x-27\right)=4212:39=108\)

\(\Rightarrow\left(3x-27\right)=195-108=87\)

\(\Rightarrow3x=87+27=114\Rightarrow x=114:3=38\)

e) \(...\Rightarrow3\left(x-2\right)=30-18=12\Rightarrow x-2=12:3=4\)

\(\Rightarrow x=4+2=6\)

Lời giải:

a.

$(\frac{-1}{3})^3.x=\frac{1}{81}=(\frac{-1}{3})^4$
$\Rightarrow x=(\frac{-1}{3})^4: (\frac{-1}{3})^3=\frac{-1}{3}$
b.

$2^2.16> 2^x> 4^2$
$\Rightarrow 2^2.2^4> 2^x> (2^2)^2$

$\Rightarrow 2^6> 2^x> 2^4$

$\Rightarrow 6> x> 4$

$\Rightarrow x=5$ (với điều kiện $x$ là số tự nhiên nhé)

c.

$9.27< 3^x< 243$

$3.3^3< 3^x< 3^5$

$\Rightarrow 3^4< 3^x< 3^5$

$\Rightarrow 4< x< 5$

Với $x$ là stn thì không có số nào thỏa mãn.

\(9.27\le\left(\frac{1}{3}\right)^x\le27.243\)

\(243\le\left(\frac{1}{3}\right)^x\le6561\)

đến đây toi tịt == 

à để xem !!! như thế này này :

\(3^5\le\left(\frac{1}{3}\right)^x\le3^8\)

Ta có \(\frac{1}{3}=0,\left(3\right)=\sqrt{3}=3\)( bt là số vô tỉ nx xem đã )

\(\Rightarrow3^5\le3^x\le3^8\)

\(\Rightarrow x=6;7\)

\(9.27\le\left(\frac{1}{3}\right)^x\le27.243\)

\(\Rightarrow3^2.3^3\le\left(\frac{1}{3}\right)^x\le3^3.3^5\)

\(\Rightarrow3^5\le\left(\frac{1}{3}\right)^x\le3^8\)

\(\Rightarrow x\in\left\{-5;-6;-7;-8\right\}\)

a) \(5^{x+3}+5^{x+1}-5^x=645\)

\(\Rightarrow5^x.5^3+5^x.5-5^x=645\)

\(\Rightarrow5^x.\left(5^3+5-1\right)=645\)

\(\Rightarrow5^x.129=645\)

\(\Rightarrow5^x=5\)

\(\Rightarrow x=1\)

Vậy \(x=1\)

b) \(9.27\ge3^x\ge243\)

\(\Rightarrow3^2.3^3\ge3^x\ge3^5\)

\(\Rightarrow3^5\ge3^x\ge3^5\)

\(\Rightarrow5\ge x\ge5\)

\(\Rightarrow x=5\)

Vậy \(x=5\)

\(9\cdot27\le\left(\dfrac{1}{3}\right)^x\le27\cdot243\)

\(\Leftrightarrow3^5\le\left(\dfrac{1}{3}\right)^x\le3^8\)

\(\Leftrightarrow\left(\dfrac{1}{3}\right)^{-5}\ge\left(\dfrac{1}{3}\right)^x\ge\left(\dfrac{1}{3}\right)^{-8}\)

=>-5>=x>=-8

hay \(x\in\left\{-5;-6;-7;-8\right\}\)

1: A=(x-1)^2>=0

Dấu = xảy ra khi x=1

5: B=-(x^2+6x+10)

=-(x^2+6x+9+1)

=-(x+3)^2-1<=-1

Dấu = xảy ra khi x=-3

2: B=x^2+4x+4-9

=(x+2)^2-9>=-9

Dấu = xảy ra khi x=-2

6: =-(x^2-5x-3)

=-(x^2-5x+25/4-37/4)

=-(x-5/2)^2+37/4<=37/4

Dấu = xảy ra khi x=5/2

3: =x^2+x+1/4-1/4

=(x+1/2)^2-1/4>=-1/4
Dấu = xảy ra khi x=-1/2

7: =4x^2+4x+1-2

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

Dấu = xảy ra khi x=-1/2

\(\left[195-\left(3x-27\right)\right]\cdot39=4212\\ \Rightarrow195-\left(3x-27\right)=4212:39\\ \Rightarrow195-\left(3x-27\right)=108\\ \Rightarrow3x-27=195-108\\ \Rightarrow3x-27=87\\ \Rightarrow3x=87+27\\ \Rightarrow3x=114\\ \Rightarrow x=114:3\\ \Rightarrow x=38\)

\(\left[195-\left(3x-27\right)\right]\cdot39=4212\\ \Leftrightarrow195-\left(3x-27\right)=108\\ \Leftrightarrow3x-27=87\\ \Leftrightarrow3x=114\\ \Leftrightarrow x=38\)

Vậy x = 38.

[195−(3x−27)]⋅39=4212

⇒195−(3x−27)=4212:39

⇒195−(3x−27)=108

⇒3x−27=195−108

⇒3x−27=87⇒3x=87+27✿

⇒3x=114⇒x=114:3⇒x=38

1: A=(x-1)^2>=0

Dấu = xảy ra khi x=1

5: B=-(x^2+6x+10)

=-(x^2+6x+9+1)

=-(x+3)^2-1<=-1

Dấu = xảy ra khi x=-3

2: B=x^2+4x+4-9

=(x+2)^2-9>=-9

Dấu = xảy ra khi x=-2

6: =-(x^2-5x-3)

=-(x^2-5x+25/4-37/4)

=-(x-5/2)^2+37/4<=37/4

Dấu = xảy ra khi x=5/2

3: =x^2+x+1/4-1/4

=(x+1/2)^2-1/4>=-1/4
Dấu = xảy ra khi x=-1/2

7: =4x^2+4x+1-2

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

Dấu = xảy ra khi x=-1/2