a)

 \(\frac{{28}}{9} \cdot 0,7 + \frac{{28}}{9} \cdot 0,5 = \frac{{28}}{9}.\left( {0,7 + 0,5} \right)\)

b)

\(\begin{array}{l}\frac{{36}}{{13}}:4 + \frac{{36}}{{13}}:9\\ = \frac{{36}}{{13}}.\frac{1}{4} + \frac{{36}}{{13}}.\frac{1}{9}\\ = \frac{{36}}{{13}}.\left( {\frac{1}{4} + \frac{1}{9}} \right)\\ = \frac{{36}}{{13}}.\frac{{13}}{{36}} = 1\end{array}\)

 \(\begin{array}{l}\frac{{36}}{{13}}:(4 + 9)\\ = \frac{{36}}{{13}}:13\\ = \frac{{36}}{{13}}.\frac{1}{{13}}\\ = \frac{{36}}{{169}}\end{array}\)

Suy ra \(\frac{{36}}{{13}}:4 + \frac{{36}}{{13}}:9\) \( \ne \) \(\frac{{36}}{{13}}:(4 + 9)\).

1. -28 + 32

2. 50 + 21

3. (-45) + (-30)

4. x + (-80)

5. 7 + (-a)

6. -25 + a

#)Giải :

\(S=\frac{38}{25}+\frac{9}{10}-\frac{11}{15}+\frac{13}{21}-\frac{15}{28}+\frac{17}{36}-\frac{19}{45}+...-\frac{119}{4950}\)

\(S=\frac{38}{25}+\left(\frac{9}{10}-\frac{11}{15}\right)+\left(\frac{13}{21}-\frac{15}{28}\right) +\left(\frac{17}{36}-\frac{19}{45}\right)+...+\left(\frac{197}{4851}-\frac{199}{4950}\right)\)

Ta thấy : 

\(\left(\frac{9}{10}-\frac{11}{15}\right)=\frac{1}{6}=\frac{1}{\left(2.3\right)}=\frac{1}{2}-\frac{1}{3}\)

\(\left(\frac{13}{21}-\frac{15}{28}\right)=\frac{1}{12}=\frac{1}{\left(3.4\right)}=\frac{1}{3}-\frac{1}{4}\)

\(\left(\frac{17}{36}-\frac{19}{45}\right)=\frac{1}{20}=\frac{1}{\left(4.5\right)}=\frac{1}{4}-\frac{1}{5}\)

..........................................................

\(\left(\frac{197}{4851}-\frac{199}{4950}\right)=\frac{1}{2450}=\frac{1}{\left(49.50\right)}=\frac{1}{49}-\frac{1}{50}\)

\(\Rightarrow S=\frac{38}{25}+\left[\left(\frac{1}{2}-\frac{1}{3}\right)+\left(\frac{1}{3}-\frac{1}{4}\right)+\left(\frac{1}{4}-\frac{1}{5}\right)+...+\left(\frac{1}{49}-\frac{1}{50}\right)\right]\)

\(\Rightarrow S=\frac{38}{25}+\left[\frac{1}{2}-\frac{1}{50}\right]\)

\(\Rightarrow S=\frac{38}{25}+\frac{24}{50}\)

\(\Rightarrow S=2\)

                #~Will~be~Pens~#

oi dòi ơi bấm máy tính mỏi tay lun:

=-194/99 nhá

Bạn ơi đừng nghiện nữa

:v mik không nghiện :>

- Ôi dễ vãi ~~

Ta có:

\(\frac{2^{35}.45^{25}.13^{22}.35^{16}}{9^{26}.65^{22}.28^{17}.25^9}=\frac{2^{35}.\left(9.5\right)^{25}.13^{22}.\left(5.7\right)^{16}}{9^{26}.\left(5.13\right)^{22}.\left(7.4\right)^{17}.\left(5.5\right)^9}\)

\(=\frac{2^{35}.9^{25}.5^{25}.13^{22}.5^{16}.7^{16}}{9^{26}.13^{22}.5^{22}.7^{17}.4^{17}.5^9.5^9}\)

\(=\frac{2^{35}.5^3}{9.4^{17}.5^2.7}\)

\(=\frac{2^{35}.5}{9.4^{17}.7}\)

\(=\frac{2^{35}.5}{9.2^{34}.7}\)

\(=\frac{2.5}{9.7}\)

\(=\frac{10}{63}\)

p/s: - Ko chắc ~

\(\frac{2^{35}.45^{25}.13^{22}.35^{16}}{9^{26}.65^{22}.28^{17}.25^9}=\frac{2^{35}.5^{25}.9^{25}.13^{22}.5^{16}.7^{16}}{9^{26}.5^{22}.13^{22}.4^{17}.7^{17}.5^9.5^9}=\frac{2^{35}.5^3.5^7}{9.\left(2^2\right)^{17}.7.5^9}=\frac{2^{35}.5^3}{9.2^{34}.7.5^2}=\frac{2.5}{9.7}=\frac{10}{63}\)