\(3+\frac{3}{5}+\frac{3}{25}+\frac{3}{125}+\frac{3}{625}\)

\(=3\left(1+\frac{1}{5}+\frac{1}{25}+\frac{1}{125}+\frac{1}{625}\right)\)

\(=3\cdot\frac{781}{625}\)

\(=\frac{2343}{625}\)

Cảm ơn bạn rất rất nhìu nhé.

Bạn xem lại đề được không? Mình cảm giác 3² phải là 3³ !

B=\(1+3^2+3^4+...+3^{100}\)

9B=\(3^2+3^4+...+3^{100}\)

9B-B=\(\left(3^2+3^4+...+3^{102}\right)-\left(1+3^2+3^4+...+3^{100}\right)\)

8B=\(3^{102}-1\)

B=\(\left(3^{102}-1\right):8\)

C=\(1+5^3+5^6+...+5^{99}\)

125C=\(5^3+5^6+5^9+...+5^{102}\)

125C-C=\(\left(5^3+5^6+5^9+...+5^{102}\right)-\left(1+5^3+5^6+...+5^{99}\right)\)

124C=\(5^{102}-1\)

C=\(\left(5^{102}-1\right):124\)

a; 5\(\dfrac{3}{4}\) : 3 + 2\(\dfrac{1}{4}\).\(\dfrac{1}{3}\) - \(\dfrac{3}{8}\)

= \(\dfrac{23}{4}\) : 3 + \(\dfrac{9}{4}\).\(\dfrac{1}{3}\) - \(\dfrac{3}{8}\)

= \(\dfrac{23}{4}\) x \(\dfrac{1}{3}\) + \(\dfrac{3}{4}\) - \(\dfrac{3}{8}\)

= \(\dfrac{23}{12}\) + \(\dfrac{3}{4}\) - \(\dfrac{3}{8}\)

= \(\dfrac{46}{24}\) + \(\dfrac{18}{24}\) - \(\dfrac{9}{24}\)

= \(\dfrac{64}{24}\) - \(\dfrac{9}{24}\)

= \(\dfrac{55}{24}\)

a) ta có |3+5| = |3|+|5| ( vì 3 x 5 > 0)

b) ta có |(-3) + (-5)| = |-3| + |-5| ( vì (-3) x (-5)

\(a,\left(x-27\right).\left(x-3\right)=0\)

\(\Rightarrow\orbr{\begin{cases}x-27=0\\x-3=0\end{cases}}\)

\(\Rightarrow\orbr{\begin{cases}x=0+27\\x=0+3\end{cases}}\)

\(\Rightarrow\orbr{\begin{cases}x=27\\x=3\end{cases}}\)

\(b,70-5.\left(2x-3\right)=45\)

\(\Rightarrow5.\left(2x-3\right)=70-45\)

\(\Rightarrow5.\left(2x-3\right)=25\)

\(\Rightarrow2x-3=25\div5\)

\(\Rightarrow2x-3=5\)

\(\Rightarrow2x=5+3\)

\(\Rightarrow2x=8\)

\(\Rightarrow x=8\div2\)

\(\Rightarrow x=4\)

~Study well~

#KSJ

`x:3/6=5/6`

`x=5/6xx3/6`

`x=15/36`

a)  x : 3/6 = 5/6  

     x = 5/6 x 3/6

     x= 15/36