\(7^x+7^{x+2}+7^{x+3}=2751\\ \Leftrightarrow7^x.\left(1+7^2+7^3\right)=2751\\ \Leftrightarrow7^x.393=2751\\ \Leftrightarrow7^x=\dfrac{2751}{393}=7=7^1\\ Vậy:x=1\)

x = 1

\(7^x\) + \(7^{x+2}\) + \(7^{x+3}\) = 2751

\(7^x\).( 1 + 7² + 7³) = 2751

\(7^x\).393  = 2751

  7\(^x\) = 2751 : 393

 7\(^x\)  = 7

   \(x\) = 1

7x + 7�+27x+2 + 7�+37x+3 = 2751

7�7x.( 1 + 72 + 73) = 2751

7�7x.393  = 2751

  7�x = 2751 : 393

 7�x  = 7

   $x$ = 1

`Answer:`

\(7^x+7^{x+2}+7^{x+3}=2751\)

\(\Leftrightarrow7^x+7^x.7^2+7^x.7^3=2751\)

\(\Leftrightarrow7^x.\left(1+7^2+7^3\right)=2751\)

\(\Leftrightarrow7^x.393=2751\)

\(\Leftrightarrow7^x=7\)

\(\Leftrightarrow x=1\)

7 x 2 = 14       7 x 4 = 28       7 x 6 = 42       7 x 3 = 21

2 x 7 = 14       4 x 7 = 28       6 x 7 = 42       3 x 7 = 21

14 : 7 = 2       28 : 7 = 4       42 : 7 = 6       21 : 7 = 3

14 : 2 = 7       28 : 4 = 7       42 : 6 = 7       21 : 3 = 7

7 x 2 = 14

4 x 7 = 28

7 x 6 = 42

3 x 7 = 21

5 x 7 = 35

2 x 7 = 14

7 x 4 = 28

6 x 7 = 42

7 x 3 = 21

7 x 5 = 35

7 x 2 = 14

4 x 7 = 28

7 x 6 = 42

3 x 7 = 21

5 x 7 = 35

2 x 7 = 14

7 x 4 = 28

6 x 7 = 42

7 x 3 = 21

7 x 5 = 35

7 x 2 = 2 x [7]      6 x 7 = 7 x [6]        3 x 7 = [7] x 3

7 x 5 = 5 x [7]      4 x 7 = 7 x [4]        7 x 0 = [0] x 7

a: \(2^7+\left(x-3^7\right)=5^7-4^7\)

=>\(128+x-2187=78125-16384\)

=>\(x-2059=61741\)

=>\(x=61741+2059=63800\)

c: \(7^2-\left(x+15\right)=5\cdot2^2\)

=>49-(x+15)=5*4=20

=>x+15=29

=>x=14

d: 7^3-7(13-x)=14

=>343-7(13-x)=14

=>7(13-x)=343-14=329

=>13-x=47

=>x=13-47=-34

6: =>x=9/10+1/5=9/10+2/10=11/10

7: =>x=3/8-5/12=36/96-40/96=-1/24

8: =>x=7/6-5/4=14/12-15/12=-1/12

9: =>x=1/35+2/7=1/35+10/35=11/35

10: =>x=2/7-7/10=20/70-49/70=-29/70

1, \(x=-\dfrac{5}{3}-\dfrac{1}{2}=-\dfrac{10}{6}-\dfrac{3}{6}=-\dfrac{13}{6}\)

2, \(x=\dfrac{1}{3}-\dfrac{3}{5}=\dfrac{5-9}{15}=-\dfrac{4}{15}\)

4, \(x=-\dfrac{7}{9}+\dfrac{4}{3}=\dfrac{-7+12}{9}=\dfrac{5}{9}\)

5, \(x=\dfrac{5}{6}-\dfrac{7}{3}=\dfrac{5-14}{6}=-\dfrac{9}{6}=-\dfrac{3}{2}\)

6, \(x=\dfrac{9}{10}+\dfrac{1}{5}=\dfrac{9+2}{10}=\dfrac{11}{10}\)

7, \(x=\dfrac{3}{8}-\dfrac{5}{12}=\dfrac{9-10}{12}=-\dfrac{1}{12}\)

8, \(x=\dfrac{7}{6}-\dfrac{5}{4}=\dfrac{14-15}{12}=-\dfrac{1}{12}\)

9, \(x=\dfrac{1}{35}+\dfrac{2}{7}=\dfrac{1+10}{35}=\dfrac{11}{35}\)

10, \(x=-\dfrac{7}{10}+\dfrac{2}{7}=\dfrac{-49+20}{70}=\dfrac{-29}{70}\)

7 x 3 = 21

7 x 8 = 56

7 x 2 = 14

7 x 1 = 7

7 x 4 = 35

7 x 6 = 42

7 x 10 = 70

0 x 7 = 0

7 x 7 = 49

7 x 4 = 28

7 x 9 = 63

7 x 0 = 0

7x3=21

7x8=56

7x2=14

7x1=7

7x5=35

7x6=42

7x10=70

0x7=0

7x7=49

7x4=28

7x9=63

7x0=0