= (4/5 - 4-5) . 3/4 = 0 . 3/4 = 0

-3/7 + (-9)/35 + 2/-5

= -38/35

-38/35

= -3/7 + -9/35 + 2/-5

= -38/35

= 4/5 - 9/16.4/5

= 4,5.(1-9/16)

= 4,5. 7/16

= 7/20

\(\dfrac{4}{5}-\dfrac{3}{4}.\dfrac{4}{5}.\dfrac{3}{4}\)

\(=\dfrac{4}{5}-\dfrac{9}{20}\)

\(=\dfrac{16}{20}-\dfrac{9}{20}\)

\(=\dfrac{7}{20}\)

= 4/5 - 9/20

= 16/20 - 9/20

= 7/20

\(=\dfrac{3^8\cdot2^{10}\cdot5^6}{2^9\cdot3^6\cdot5^7}=3^2\cdot\dfrac{2}{5}=\dfrac{18}{5}\)

\(\dfrac{9^4\cdot4^5\cdot25^3}{8^3\cdot27^2\cdot5^7}\)

\(=\dfrac{\left(3^2\right)^4\cdot\left(2^2\right)^5\cdot\left(5^2\right)^3}{\left(2^3\right)^3\cdot\left(3^3\right)^2\cdot5^7}\)

\(=\dfrac{3^8\cdot2^{10}\cdot5^6}{2^9\cdot3^6\cdot5^7}\)

\(=\dfrac{3^2\cdot2\cdot1}{1\cdot1\cdot5}\)

\(=\dfrac{18}{5}\)

Tần số sóng trên dây càng lớn, số bụng sóng càng nhiều. Số bụng sóng tỉ lệ với tần số sóng.

\(\dfrac{3}{4}\cdot26\dfrac{1}{5}-\dfrac{3}{4}\cdot4\dfrac{1}{5}=\dfrac{3}{4}\cdot\left(26\dfrac{1}{5}-4\dfrac{1}{5}\right)=\dfrac{3}{4}\cdot22=\dfrac{33}{2}\)