\(15-15:15+15\)
\(=15-1+15\)
\(=29\)

Vì 0 chia cho số nào cũng bằng 0 nên
\(x\in\left\{1;2;3;4;........\right\}\)

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

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