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\(17,58\times43+5,7\times175,8\)
\(=17,58\times43+5,7\times10\times17,58\)
\(=17,58\times43+57\times17,58\)
\(=17,58\times\left(43+57\right)\)
\(=17,58\times100\)
\(=1758\)
_Chúc bạn học tốt_
\(17,58\times43+5,7\times175,8=17,58\times10\times4,3+5,7\times175,8\)
\(=175,8\times4,3+5,7\times175,8\)
\(=175,8\times\left(4,3+5,7\right)=175,8\times10=1758\)
\(-\frac{9}{11}\cdot\frac{3}{8}-\frac{9}{11}\cdot\frac{5}{8}+\frac{17}{11}=-\frac{9}{11}\left(\frac{3}{8}+\frac{5}{8}\right)+\frac{17}{11}=-\frac{9}{11}\cdot1+\frac{17}{11}=1\)
\(\frac{2}{1.3}+....+\frac{2}{53.55}=1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+...+\frac{1}{53}-\frac{1}{55}=1-\frac{1}{55}=\frac{54}{55}\)
\(x+5-\frac{1}{2}=3\frac{1}{2}\)
\(x+5=3.5+0.5=4\)
\(x=4-5=-1\)
\(3^{x+1}=27=3^3\)
\(x+1=3\)
vậy x=2
Trả lời
b)(1/3+12/67+13/41)-(79/67-28/41)
=1/3+12/67+13/41-79/67+28/41
=1/3+(12/67-79/67)+(13/41+28/41)
=1/3+(-67/67)+41/41
=1/3+(-1)+1
=1/3+0
=1/3.
45 × 16 - 17 / 28 + 45 × 15
= 45 × (15 + 1) - 17 / 28 + 45 × 15
= 45 × 15 + (45 - 17) / 28 + 45 × 15
= 45 × 15 + 28 / 28 + 45 × 15
= 1
\(\frac{45\times16-17}{28+45\times15}\)
\(=\frac{45\left(15+1\right)-17}{28+45\times15}\)
\(=\frac{45\times15+\left(45-17\right)}{28+45\times15}\)
\(=\frac{45\times15+28}{28+45\times15}\)
\(=1\)
Đặt \(A=\frac{1}{3}+\frac{1}{3^2}+\frac{1}{3^3}+...+\frac{1}{3^8}\)
\(\Leftrightarrow\)\(3A=1+\frac{1}{3}+\frac{1}{3^2}+...+\frac{1}{3^7}\)
\(\Leftrightarrow\)\(3A-A=\left(1+\frac{1}{3}+\frac{1}{3^2}+...+\frac{1}{3^7}\right)-\left(\frac{1}{3}+\frac{1}{3^2}+\frac{1}{3^3}+...+\frac{1}{3^8}\right)\)
\(\Leftrightarrow\)\(2A=1-\frac{1}{3^8}\)
\(\Leftrightarrow\)\(2A=\frac{3^8-1}{3^8}\)
\(\Leftrightarrow\)\(A=\frac{3^8-1}{3^8}:2\)
\(\Leftrightarrow\)\(A=\frac{3^8-1}{3^8}.\frac{1}{2}\)
\(\Leftrightarrow\)\(A=\frac{3^8-1}{2.3^8}\)
b) Đặt \(A=\frac{1}{3}+\frac{1}{3^2}+\frac{1}{3^3}+.....+\frac{1}{3^8}\)
\(\Rightarrow\)\(3A=1+\frac{1}{3}+\frac{1}{3^2}+....+\frac{1}{3^7}\)
\(\Rightarrow\)\(3A-A=\left(1+\frac{1}{3}+\frac{1}{3^2}+...+\frac{1}{3^7}\right)-\left(\frac{1}{3}+\frac{1}{3^2}+\frac{1}{3^3}+....+\frac{1}{3^8}\right)\)
\(\Rightarrow\)\(2A=1-\frac{1}{3^8}\)
\(\Rightarrow\)\(A=\frac{1-\frac{1}{3^8}}{2}\)