Question

Giúp minh câu 16,17,18,19,20,21,22,23,24,25,26 với.

Answer 1

16.

\(A=\dfrac{16^2.16^3}{4^8}=\dfrac{4^4.4^6}{4^8}=\dfrac{4^{10}}{4^8}=4^2=16\)

\(B=\dfrac{8^2.8^3}{2^{11}}=\dfrac{2^6.2^9}{2^{11}}=\dfrac{2^{15}}{2^{11}}=2^4=16\)

17. 

\(6,673\)

18.

\(\Rightarrow x=\dfrac{-3}{5}.15=-9\)

19.

\(x=12:\dfrac{3}{4}=16\)

20.Áp dụng t/c dtsbn ta có;

\(\dfrac{x}{8}=\dfrac{y}{12}=\dfrac{x+y}{8+12}=\dfrac{40}{20}=2\)

\(\dfrac{x}{8}=2\Rightarrow x=16\\ \dfrac{y}{12}=2\Rightarrow y=24\)

21.

Áp dụng t/c dtsbn ta có;

\(\dfrac{x}{4}=\dfrac{y}{9}=\dfrac{x-y}{4-9}=\dfrac{15}{-5}=-3\)

\(\dfrac{x}{4}=-3\Rightarrow x=-12\\ \dfrac{y}{9}=-3\Rightarrow y=-27\)

22.

gọi số học sinh nam, nữ lần lượt là a,b

Ta có: \(\left\{{}\begin{matrix}\dfrac{a}{6}=\dfrac{b}{7}\\a+b=39\end{matrix}\right.\)

Áp dụng t/c dtsbn ta có;

\(\dfrac{a}{6}=\dfrac{b}{7}=\dfrac{a+b}{6+7}=\dfrac{39}{13}=3\)

\(\dfrac{a}{6}=3\Rightarrow a=18\\ \dfrac{b}{7}=3\Rightarrow b=21\)

Vậy ...

23.\(\sqrt{16}=4\)

24.\(\sqrt{x}=5\Rightarrow x=25\)

25.B

26.A