cho S=\(\frac{3}{1\cdot4}\)+\(\frac{3}{4\cdot7}\)+\(\frac{3}{7\cdot10}\)+.....+\(\frac{3}{40\cdot43}\)+\(\frac{3}{43\cdot46}\).hãy chứng tỏ rằng S nhỏ hơn 1
Hãy nhập câu hỏi của bạn vào đây, nếu là tài khoản VIP, bạn sẽ được ưu tiên trả lời.
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
a) \(\frac{x}{3}-\frac{1}{4}=\frac{-5}{6}\)
\(\Rightarrow\frac{x}{3}=\frac{-5}{6}+\frac{1}{4}\)
\(\Rightarrow\frac{x}{3}=\frac{-7}{12}\)
\(\Rightarrow x=\frac{\left(-7\right).3}{12}\)
\(\Rightarrow x=\frac{-7}{4}\)
Vậy x = \(\frac{-7}{4}\)
b) \(\frac{x+3}{15}=\frac{1}{3}\)
\(\Rightarrow\left(x+3\right).3=15\)
\(\Rightarrow x+3=15:3\)
\(\Rightarrow x+3=5\)
\(\Rightarrow x=5-3\)
\(\Rightarrow x=2\)
Vậy x = 2
c) \(\frac{x-12}{4}=\frac{1}{2}\)
\(\Rightarrow\left(x-12\right).2=4\)
\(\Rightarrow x-12=4:2\)
\(\Rightarrow x-12=2\)
\(\Rightarrow x=2+12\)
\(\Rightarrow x=14\)
Vậy x = 14
d) \(\frac{25}{9}-\frac{12}{13}x=\frac{7}{9}\)
\(\Rightarrow\frac{12}{13}x=\frac{25}{9}-\frac{7}{9}\)
\(\Rightarrow\frac{12}{13}x=2\)
\(\Rightarrow x=2:\frac{12}{13}\)
\(\Rightarrow x=\frac{13}{6}\)
Vậy x = \(\frac{13}{6}\)
_Chúc bạn học tốt_
a)\(\frac{x}{3}-\frac{1}{4}=-\frac{5}{6}\)
\(\frac{x}{3}=-\frac{5}{6}+\frac{1}{4}\)
\(\frac{x}{3}=-\frac{7}{12}\)
\(x=-\frac{7}{12}\times3\)
\(\Rightarrow x=-\frac{7}{4}\)
b) \(\frac{x+3}{15}=\frac{1}{3}\)
\(\frac{x+3}{15\div5}=\frac{1}{3}\)
\(\Rightarrow x=5-3\)
\(\Rightarrow x=2\)
c) \(\frac{x-12}{4}=\frac{1}{2}\)
\(\frac{x-12}{4\div2}=\frac{1}{2}\)
\(x=12+2\)
\(\Rightarrow x=14\)
d) tự làm nhé cũng dễ mà
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
Vì góc cBa kề bù với góc cBd
Suy ra cBa+cBd=aBd=180 độ
Suy ra cBa=180độ-cBd
Mà cBd=120 độ
Suy ra cBd=180-120=60 độ
Trên cùng nửa mặt phẳng bờ là tia ad có cBd>dBm
Suy ra Bc là tia nằm giữa
Suy ra dBm+mBc=cBd
Suy ra cBm=cBd-dBm
Mà dBm=30độ(1),cBd=60độ(2)
Suy ra cBm=60-30=30(3)
Từ (1),(2),(3)
Suy ra dBm=cBm=cbd:2=60:2=30độ
Suy ra Bm là tia phân giác của dBd
![](https://rs.olm.vn/images/avt/0.png?1311)
a) \(49^{12}\)và \(5^{40}\)
\(49^{12}=\left(49^3\right)^4=\left(\left(7^2\right)^3\right)^4=\left(7^6\right)^4\)
\(5^{40}=\left(5^{10}\right)^4\)
\(7^6=\left(7^3\right)^2>\left(5^5\right)^2\)vì \(7^2\cdot7>5^3\cdot5^2\)
\(\Rightarrow49^{12}< 5^{40}\)
\(\left(-\frac{1}{16}\right)^{100}=\left(-\left(\frac{-1}{2}\right)^4\right)^{100}\)
\(=\left(-\frac{1}{2}\right)^{400}< \left(-\frac{1}{2}\right)^{500}\)
\(^{\frac{3}{1\cdot4}+\frac{3}{4\cdot7}+\frac{3}{7\cdot10}+...+\frac{3}{40\cdot43}+\frac{3}{43\cdot46}}\)
\(1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+...+\frac{1}{10}-\frac{1}{43}+\frac{1}{43}-\frac{1}{46}\)
\(1-\frac{1}{46}=\frac{45}{46}\)
Vì \(1-\frac{1}{46}< 1\)nên \(\frac{3}{1\cdot4}+\frac{3}{4\cdot7}+\frac{3}{7\cdot10}+...+\frac{3}{40\cdot43}+\frac{3}{43\cdot46}< 1\)
Chúc bạn học tốt
\(S=\frac{3}{1\cdot4}+\frac{3}{4\cdot7}+\frac{3}{7\cdot10}+...+\frac{3}{40\cdot43}\)
\(S=1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+...+\frac{1}{40}-\frac{1}{43}\)
\(S=1-\frac{1}{43}\)
\(S=\frac{42}{43}< 1\)