\(3+\frac{2}{5}=3\frac{2}{5}=\frac{17}{5}.\)

\(4-\frac{5}{7}=\frac{4}{1}-\frac{5}{7}=\frac{28}{7}-\frac{5}{7}=\frac{23}{7}.\)

\(1-\left(\frac{2}{5}+\frac{1}{3}\right)=1-\left(\frac{6}{15}+\frac{5}{15}\right)=1-\frac{11}{15}=\frac{4}{15}.\)

1. \(\left(3x-1\right)^2=25\)

\(\Rightarrow\orbr{\begin{cases}3x-1=\sqrt{25}\\3x-1=-\sqrt{25}\end{cases}}\Rightarrow\orbr{\begin{cases}3x=6\\3x=-4\end{cases}}\Rightarrow\orbr{\begin{cases}x=2\\x=-\frac{4}{3}\end{cases}}\)

2. \(5^{14}=\left(5^2\right)^7=25^7\)

Vì: \(25< 27\Rightarrow5^{14}< 27^7\)

123 + 200 + 50 + 50 = 423

1,2,3,..,10

= (10 - 1)/1+1

= 10

tổng = (10+1)x10/2

=52

2 . ( x + 4 ) = 12

x + 4 = 12 : 2

x + 4 = 6

x = 6 - 4 

x = 2