1.

=3/5x(3/7+4/7)+2/5x(13/9-4/9)

=3/5x1+2/5x1

=3/5+2/5

=1

2.Xx(3/4+4/5)=7/10

Xx31/20=7/10

X         =7/10:31/20

X         =14/31

\(\frac{3}{5}\cdot\frac{3}{7}+\frac{3}{5}\cdot\frac{4}{7}+\frac{2}{5}\cdot\frac{13}{9}-\frac{2}{5}\cdot\frac{4}{9}\)

\(=\frac{3}{5}\cdot\left(\frac{3}{7}+\frac{4}{7}\right)+\frac{2}{5}\cdot\left(\frac{13}{9}-\frac{4}{9}\right)\)

\(=\frac{3}{5}\cdot1+\frac{2}{5}\cdot1\)\(=\frac{3}{5}+\frac{2}{5}=1\)

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\(\frac{3}{4}\cdot x+\frac{4}{5}\cdot x=\frac{7}{10}\)

\(\left(\frac{3}{4}+\frac{4}{5}\right)\cdot x=\frac{7}{10}\)

\(\frac{31}{20}\cdot x=\frac{7}{10}\)

\(x=\frac{7}{10}:\frac{31}{20}\)

\(x=\frac{14}{31}\)

2x - 3 = 5⁴ : 5²

2x - 3 = 5^{4 - 2} = 5² = 25

2x = 25 + 3

2x = 28

x = 28 : 2

x = 14

5^{x + 2} = 5³ . 125

5^{x + 2} = 5³ . 5³ = 5^{3 + 3} = 5⁶

=> x = 6 - 2

x = 4

2x-3 =5^4 :5^2

2x - 3 = 5^2 

2x-3 = 25 

2x =22

x = 11

5 ^x+2 = 5^3 x 125

5^x+2  =5^3 x 5^3

5^x+2  = 5^9

x+2 =9

x  = 7

a, 2x - 3 = 5^4 : 5^2

2x - 3 = 25

2x       = 25 + 3

2x         = 28

x           = 28 : 2

x            = 14

b, 5^x+2 = 5³ . 125     ( đổi 125 = 5³ )

    5^x+2 = 5⁶

    x + 2 = 6

     x = 6 - 2 = 4

(3/5+5/8)+(3/4+1/2)=49/40+5/4=99/40

(9+1)+(8+2)+(7+3)+(6+4)+10+5

=10+10+10+10+10+5=45

9+3+2+1+7+8+5+10+6+4= (9+1)+(2+8)+(3+7)+(4+6)+5=10+10+10+10+5=10.4+5=40+5=45

(9+1)+(3+7)+(2+8)+(6+4)+10

=10+10+10+10+10

=50

a; 5\(\dfrac{3}{4}\) : 3 + 2\(\dfrac{1}{4}\).\(\dfrac{1}{3}\) - \(\dfrac{3}{8}\)

= \(\dfrac{23}{4}\) : 3 + \(\dfrac{9}{4}\).\(\dfrac{1}{3}\) - \(\dfrac{3}{8}\)

= \(\dfrac{23}{4}\) x \(\dfrac{1}{3}\) + \(\dfrac{3}{4}\) - \(\dfrac{3}{8}\)

= \(\dfrac{23}{12}\) + \(\dfrac{3}{4}\) - \(\dfrac{3}{8}\)

= \(\dfrac{46}{24}\) + \(\dfrac{18}{24}\) - \(\dfrac{9}{24}\)

= \(\dfrac{64}{24}\) - \(\dfrac{9}{24}\)

= \(\dfrac{55}{24}\)