\(a,3^{x+2}-3^{x-1}=702\)
\(3^x.3^2-3^x:3^1=702\)
\(3^x.9-3^x.\dfrac{1}{3}=702\)
\(3^x.\left(9-\dfrac{1}{3}\right)=702\)
\(3^x.\dfrac{26}{3}=702\)
\(3^x=702:\dfrac{26}{3}\)
\(3^x=81\)
\(3^x=3^4\)
\(x=4\)
Vậy .... 

 

\(2+\dfrac{1}{3}-\dfrac{7}{5}=\dfrac{30}{15}+\dfrac{5}{15}-\dfrac{21}{15}=\dfrac{30+5-21}{15}=\dfrac{14}{15}\)

à ha, h cj ms để ý bình luận của bn này 

*** là j v ạ?

C

c) 6,15 + 8,75 + 3,75 + 1,25
= ( 6,15 + 3,75) + ( 8,75 + 1,25)
= 9,9 + 10
= 19,9
d) 0,215 x 74,24 + 25,76 x 0,215 + 18,5
= 0,215 x ( 74,24 + 25,76) + 18,5
= 0,215 x 100 + 18,5
= 21,5 + 18,5
= 40
e) \(\dfrac{3}{7}:\dfrac{11}{5}+\dfrac{4}{7}:\dfrac{11}{5}\)
 = \(\dfrac{3}{7}\times\dfrac{5}{11}+\dfrac{4}{7}\times\dfrac{5}{11}\)
= \(\dfrac{5}{11}\times\left(\dfrac{3}{7}+\dfrac{4}{7}\right)\)

= \(\dfrac{5}{11}\times1\)
= \(\dfrac{5}{11}\)
 

a) 6,15 : 0,5 + 6,15 : 0,2 + 3 x 6,15
= 6,15 x 2 + 6,15 . 5 + 3 x 6,15
= 6,15 x ( 2 + 5 + 3)
= 6,15 x 10
= 61,5

???

   \(\dfrac{1}{1.2}+\dfrac{1}{2.3}+\dfrac{1}{3.4}+...+\dfrac{1}{8.9}+\dfrac{1}{9.10}\)
= \(1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+...+\dfrac{1}{8}-\dfrac{1}{9}+\dfrac{1}{9}-\dfrac{1}{10}\)
= \(1-\dfrac{1}{10}\)
\(=\dfrac{9}{10}\)

       \(\dfrac{3}{1.4}+\dfrac{3}{4.7}+\dfrac{3}{7.10}+...+\dfrac{3}{94.97}+\dfrac{3}{97.100}\)
3A = 3.\(\left(\dfrac{1}{1.4}+\dfrac{1}{4.7}+\dfrac{1}{7.10}+...+\dfrac{1}{94.97}+\dfrac{1}{97.100}\right)\)
3A = 3.\(\left(1-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{10}+...+\dfrac{1}{94}-\dfrac{1}{97}+\dfrac{1}{97}-\dfrac{1}{100}\right)\)
3A = 3.\(\left(1-\dfrac{1}{100}\right)\)
3A = 3.\(\dfrac{99}{100}\)
3A = \(\dfrac{297}{100}\)
  A = \(\dfrac{297}{100}:3\)
  A = \(\dfrac{297}{100}.\dfrac{1}{3}\)
  A = \(\dfrac{99}{100}\)