a.\(\left(3\frac{1}{2}+2x\right).2\frac{2}{3}=5\frac{1}{3}\)
b, \(|2x+3|=5\)
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trả lời câu hỏi trên hỏi đáp và phải cs người trên 12 đ tk đúng cho mk
Đặt \(A=\frac{10^{1990}+1}{10^{1991}+1}\)
\(\Rightarrow10A=\frac{10\cdot(10^{1990}+1)}{10^{1991}+1}\)
\(=\frac{10^{1991}+10}{10^{1991}+1}=\frac{10^{1991}+1+9}{10^{1991}+1}=1+\frac{9}{10^{1991}+1}\)
Đặt \(B=\frac{10^{1991}+1}{10^{1992}+1}\)
\(\Rightarrow10B=\frac{10\cdot(10^{1991}+1)}{10^{1992}+1}=\frac{10^{1992}+10}{10^{1992}+1}=\frac{10^{1992}+1+9}{10^{1992}+1}=1+\frac{9}{10^{1992}+1}\)
Tự so sánh được rồi -_-
Help Me
Tui cần gấp
Đúng tui k nhưng làm hẳn ra nha :)
Nếu lâu thì làm mẫu 1 vài phần OK :)
a) \(2A=2^1+2^2+2^3+...+2^{2010}\)
=> \(2A-A=2^{2011}-2^0\Leftrightarrow A=2^{2011}-1\)
b) \(3B=3+3^2+3^3+3^4+...+3^{101}\)
=> \(3B-B=3^{101}-1\Leftrightarrow2B=3^{101}-1\Leftrightarrow B=\frac{1}{2}\left(3^{101}-1\right)\)
Tương tự Cx4, Dx5
\(C=\frac{3}{3\cdot5}+\frac{3}{5\cdot7}+...+\frac{3}{2013\cdot2015}\) mới đúng nhé :">
Ta có: \(C=\frac{3}{3\cdot5}+\frac{3}{5\cdot7}+...+\frac{3}{2013\cdot2015}\)
\(\Rightarrow\frac{3}{2}C=\frac{2}{3\cdot5}+\frac{2}{5\cdot7}+...+\frac{2}{2013\cdot2015}\)
\(\Rightarrow\frac{3}{2}C=\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{2013}-\frac{1}{2015}\)
\(\Rightarrow\frac{3}{2}C=\frac{1}{3}-\frac{1}{2015}=\frac{2015}{6045}-\frac{1}{6045}\)
\(\Rightarrow C=\frac{2014}{6045}:\frac{3}{2}=\frac{2014}{5045}\cdot\frac{2}{3}=\frac{4028}{15135}\)
\(C=\frac{3}{3.5}+\frac{3}{5.7}+\frac{3}{7.9}+...+\frac{3}{2013.2015}\)
\(=\frac{3}{2}\left(\frac{2}{3.5}+\frac{2}{5.7}+\frac{2}{7.9}+...+\frac{2}{3013.2015}\right)\)
\(=\frac{3}{2}\left(\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+...+\frac{1}{2013}-\frac{1}{2015}\right)\)
\(=\frac{3}{2}\left(\frac{1}{3}-\frac{1}{2015}\right)\)
\(=\frac{3}{2}.\frac{2014}{6045}\)
\(=\frac{4028}{15135}\)
Study well ! >_<
5290 cm\(^2\)= 0.529 m\(^2\) 72780 m\(^2\) = 7.278 hm\(^2\)
3.2 dam \(^2\)= 320 m\(^2\) 1403 dam\(^2\) = 14.03 hm
0.5 km\(^2\) = 500000 m\(^2\) 20.68 dam\(^2\) = 0.2068 hm\(^{^2}\)
0.15 ha = 1500 m\(^2\)
\(\left(3\frac{1}{2}+2x\right).2\frac{2}{3}=5\frac{1}{3}\)
\(\Rightarrow\left(\frac{7}{2}+2x\right)\cdot\frac{8}{3}=\frac{16}{3}\)
\(\Rightarrow\frac{7}{2}+2x=\frac{16}{3}\div\frac{8}{3}\)
\(\Rightarrow\frac{7}{2}+2x=\frac{16}{3}\cdot\frac{3}{8}\)
\(\Rightarrow\frac{7}{2}+2x=2\Rightarrow2x=2-\frac{7}{2}\Rightarrow2x=-\frac{3}{2}\)
\(\Rightarrow x=\frac{-3}{2}\div2\Rightarrow x=-\frac{3}{2}\cdot\frac{1}{2}=-\frac{3}{4}\)
b, \(\left|2x+3\right|=5\)
\(\Rightarrow\orbr{\begin{cases}2x+3=5\\2x+3=-5\end{cases}}\)
\(\Rightarrow\orbr{\begin{cases}2x=2\\2x=-8\end{cases}\Rightarrow\orbr{\begin{cases}x=1\\x=-4\end{cases}}}\)
a) (3 1/2 + 2x ) . 2 2/3 = 5 1/5
( 7/2 + 2x) . 8/3= 16/3
7/2 + 2x = 16/3 : 8/3
7/2 + 2x = 2
2x = 2- 7/2
2x = -3/2
x = -3/2 : 2
x = -3/4