Tổng vận tốc của người đó là: 10 + 30 = 40 ( km/ h )

Quãng đường AB dài là: 40 * 8 = 320 ( km )

Đáp số: 320 km

Chú ý: Dấu * là dấu nhân nhé!

CHÚC BẠN VUI VẺ

aaa = a x 111 = a x3 x 37 luôn chia hết cho 37

là số

71,73,79

\(\sqrt{x+1}=x-2\)

a) \(\frac{3n+2}{n-1}=\frac{3n-3+5}{n-1}=\frac{3\left(n-1\right)+5}{n-1}=3+\frac{5}{n-1}\)

\(\Rightarrow n-1\inƯ\left(5\right)\Rightarrow n-1\in\left\{-5;-1;1;5\right\}\Rightarrow n\in\left\{-4;0;2;6\right\}\)

b) \(\frac{3n-24}{n-4}=\frac{3n-12-12}{n-4}=\frac{3\left(n-4\right)-12}{n-4}=3+\frac{12}{n-4}\)

\(\Rightarrow n-4\inƯ\left(12\right)\Rightarrow n-4\in\left\{-12;-6;-4;-3;-2;-1;1;2;3;4;6;12\right\}\)

\(\Rightarrow n\in\left\{-8;-2;0;1;2;3;5;6;7;8;10;16\right\}\)

c) \(\frac{n^2+5}{n+1}=\frac{n\left(n+1\right)-\left(n+1\right)+6}{n+1}=n-1+\frac{6}{n+1}\)

\(\Rightarrow n+1\inƯ\left(6\right)\Rightarrow n+1\in\left\{-6;-3;-2;-1;1;2;3;6\right\}\Rightarrow n\in\left\{-7;-4;-3;-2;0;1;2;5\right\}\)

\(\frac{1}{\sqrt{1}}=1\)

\(\frac{1}{\sqrt{2}}+\frac{1}{\sqrt{3}}>\frac{1}{\sqrt{4}}+\frac{1}{\sqrt{4}}=\frac{2}{\sqrt{4}}=1\)

\(\frac{1}{\sqrt{4}}+\frac{1}{\sqrt{5}}+\frac{1}{\sqrt{6}}+\frac{1}{\sqrt{7}}+\frac{1}{\sqrt{8}}>5\cdot\frac{1}{\sqrt{9}}=\frac{5}{3}>1\)

\(\frac{1}{\sqrt{9}}+\frac{1}{\sqrt{10}}+\frac{1}{\sqrt{11}}+...+\frac{1}{\sqrt{15}}>7\cdot\frac{1}{\sqrt{16}}=\frac{7}{4}>1\)

\(\frac{1}{\sqrt{16}}+\frac{1}{\sqrt{17}}+...+\frac{1}{\sqrt{25}}>10\cdot\frac{1}{\sqrt{25}}=2>1\)

Cộng từng vế ta có:

\(\frac{1}{\sqrt{1}}+\frac{1}{\sqrt{2}}+\frac{1}{\sqrt{3}}+...+\frac{1}{\sqrt{25}}>5\)đpcm

22-2-2=20
ủng hộ mk với