Xin lỗi,em không giúp được 

2-4+4,4-4.7+7.65-78+87= 14,35

Câu 3: 

\(3^{417}>3^{400}=\left(3^4\right)^{100}=81^{100}\)

\(4^{278}< 4^{300}=\left(4^3\right)^{100}=64^{100}\)

Có \(81>64\)nên \(81^{100}>64^{100}\)

Suy ra \(3^{417}>4^{278}\).

Câu 4: 

\(A=5^{x+1}+5^{x+2}+5^{x+3}+...+5^{x+120}\)

\(=5^x\left(5+5^2+...+5^{119}\right)\)

\(=5^x\left[\left(5+5^2+5^3+5^4\right)+...+\left(5^{117}+5^{118}+5^{119}+5^{120}\right)\right]\)

\(=5^x\left[\left(5+5^2+5^3+5^4\right)+...+5^{116}\left(5+5^2+5^3+5^4\right)\right]\)

\(=5^x\left(1+...+5^{116}\right)\left(5+5^2+5^3+5^4\right)=5^x\left(1+...+5^{116}\right).780\)

chia hết cho \(780\). 

a) \(\frac{1}{8}-\left(x-\frac{1}{2}\right)=\frac{1}{\sqrt{9}}\)

\(\Rightarrow\frac{1}{8}-\left(x-\frac{1}{2}\right)=\frac{1}{3}\)

\(\Rightarrow x-\frac{1}{2}=\frac{1}{8}-\frac{1}{3}\)

\(\Rightarrow x-\frac{1}{2}=\frac{-5}{24}\)

\(\Rightarrow x=\frac{7}{24}\)

b) \(\left|\frac{5}{18}-x\right|+\frac{1}{5}=\frac{1}{2}\)

\(\Rightarrow\left|\frac{5}{18}-x\right|=\frac{3}{10}\)

\(\Rightarrow\orbr{\begin{cases}\frac{5}{18}-x=\frac{3}{10}\\\frac{5}{18}-x=-\frac{3}{10}\end{cases}}\Rightarrow\orbr{\begin{cases}x=\frac{5}{18}-\frac{3}{10}\\x=\frac{5}{18}+\frac{3}{10}\end{cases}}\Rightarrow\orbr{\begin{cases}x=\frac{-1}{45}\\x=\frac{26}{45}\end{cases}}\)

~ Chúc bạn ho tốt ~ !!!!!!!!!!!!

nhanh vậy 

là 24 người thì phải