cái này liớp 6 em lớp 5 sorry chj nhak

Ta có:
A = (457/1 + 1) + (456/2 + 1) + ... + (2/456 + 1) + (1/457 + 1) - 457
A = 458 + 458/2 + ... + 458/456 + 458/457 - 457
A = 458 (1 + 1/2 + ...+ 1/456 + 1/457) - 457
Xét 1 + 1/2 + ... + 1/456 + 1/457, ta có
1 = 1
1/2 = 1/2
1/3 + 1/4 > 1/4 + 1/4 = 1/2
1/5 + 1/6 + ... + 1/8 > 1/8 + 1/8 + ... + 1/8 = 1/2
1/9 + 1/10 +...+ 1/16 > 1/16 + 1/16 +...+ 1/16 = 1/2
1/17 + 1/18 + ... + 1/32 > 1/32 + ... + 1/32 = 1/2
1/33+ 1/34 + ... + 1/64 > 1/64 + ...+ 1/64 = 1/2
1/65 + 1/66 + ...+ 1/128 > 1/128 + ... + 1/128 = 1/2
1/129 + 1/130 + ... + 1/256 > 1/256 + ...+ 1/256 = 1/2
1/257 + 1/258 + ... + 1/457 > 1/457 + ... + 1/457 = 201/457 > 0,4
Vậy 1 + 1/2 + ... + 1/456 + 1/457 > 1 + 1/2 + 1/2 + 1/2 + 1/2 + 1/2 + 1/2 + 1/2 + 1/2 + 0,4 = 5,4
Vậy A > 458*5,4 - 457 = 2016,2
Vậy A > 2016.
 

Ta có:
A = (456/2 + 1) + ... + (2/456 + 1) + (1/457 + 1) + 1
A = 458 + 458/2 + ... + 458/456 + 458/457 - 458/458
A = 458 (1/2 + ...+ 1/456 + 1/457 + 1/458)
Xét 1/2 + ... + 1/456 + 1/458, ta có
1/2 = 1/2
1/3 + 1/4 > 1/4 + 1/4 = 1/2
1/5 + 1/6 + ... + 1/8 > 1/8 + 1/8 + ... + 1/8 = 1/2
1/9 + 1/10 +...+ 1/16 > 1/16 + 1/16 +...+ 1/16 = 1/2
1/17 + 1/18 + ... + 1/32 > 1/32 + ... + 1/32 = 1/2
1/33+ 1/34 + ... + 1/64 > 1/64 + ...+ 1/64 = 1/2
1/65 + 1/66 + ...+ 1/128 > 1/128 + ... + 1/128 = 1/2
1/129 + 1/130 + ... + 1/256 > 1/256 + ...+ 1/256 = 1/2
1/257 + 1/258 + ... + 1/458 > 1/458 + ... + 1/458 = 202/458
Vậy 1/2 + ... + 1/456 + 1/457 > 1/2 + 1/2 + 1/2 + 1/2 + 1/2 + 1/2 + 1/2 + 1/2 + 202/458 = 4 + 202/458 = 2034/458
Vậy A > 458*2034/458 = 2034
Vậy A > 2016. 

\(\left(2^2\div4\right).2^n=4\)

\(\Leftrightarrow\left(4\div4\right).2^n=4\)

\(\Leftrightarrow1.2^n=4\)

\(\Leftrightarrow2^n=4\)

\(\Leftrightarrow2^n=2^2\)

\(\Rightarrow n=2\)

Vậy \(n=2\)

\(1+2+3+4+...+n=190\)

Ta có:

\(\Leftrightarrow\left(n+1\right)n\div2=190\)

\(\Leftrightarrow\left(n+1\right)n=190.2\)

\(\Leftrightarrow\left(n+1\right)n=380\)

\(\Leftrightarrow\left(n+1\right)n=19.20\)

\(\Rightarrow n=19\)

Vậy \(n=19\)

\(\frac{x}{134}=\frac{9}{7}\cdot\frac{5}{-11}\)

\(\frac{x}{134}=\frac{9\cdot\left(-5\right)}{7\cdot11}\)

\(\frac{x}{134}=\frac{-45}{77}\)

Để A là PS thì \(n\in Z\)và \(n+4\ne0\) \(=>n\ne4\)

Vậy để A là Ps thì \(n\ne-4\)

@minh

em lạy anh đấy cho em chơi chung vs chứ em ko có ai chơi chung cả

Ta có:

\(\hept{\begin{cases}a⋮12\\b⋮12\end{cases}}\Rightarrow a-b⋮12=48\)

\(\Rightarrow\hept{\begin{cases}a=48\cdot2\\b=48\end{cases}}\)

\(\Rightarrow\hept{\begin{cases}a=96\\b=48\end{cases}}\)