\(\dfrac{1}{3\cdot1803}\)+\(\dfrac{1}{4\cdot1804}\)+...+\(\dfrac{1}{62\cdot1862}\)
\(\dfrac{1}{3\cdot63}\)+\(\dfrac{1}{4\cdot64}\)+...+\(\dfrac{1}{1802\cdot1862}\)
Chứng tỏ rằng:
\(1+\dfrac{1}{2}+\dfrac{1}{3}+...+\dfrac{1}{62}+\dfrac{1}{63}+\dfrac{1}{64}>4\)
A=\(\dfrac{2}{3}\)+\(\dfrac{14}{15}\)+\(\dfrac{34}{35}\)+\(\dfrac{62}{63}\)+\(\dfrac{98}{99}\)+\(\dfrac{142}{143}\)+\(\dfrac{194}{195}\)
Và B=5+\(\dfrac{1}{2^2}\)+\(\dfrac{1}{3^3}\)+\(^{\dfrac{1}{4^4}}\)+\(\dfrac{1}{5^5}\)+\(\dfrac{1}{6^6}\)+\(\dfrac{1}{7^7}\).So sánh A và B
K = \(\left(3\dfrac{1}{3}.1,9+9,5:4\dfrac{1}{3}\right).\left(\dfrac{62}{75}-\dfrac{4}{25}\right)\)
\(K=\left(\dfrac{10}{3}\cdot\dfrac{19}{10}+\dfrac{19}{2}:\dfrac{13}{3}\right)\cdot\dfrac{2}{3}\)
\(=\dfrac{665}{117}\)
\(K=\left(\dfrac{10}{3}\cdot\dfrac{19}{10}+\dfrac{19}{2}:\dfrac{13}{3}\right)\cdot\left(\dfrac{62}{75}-\dfrac{12}{25}\right)=\left(\dfrac{19}{3}+\dfrac{57}{26}\right)\cdot\dfrac{2}{3}=\dfrac{665}{78}\cdot\dfrac{2}{3}=\dfrac{665}{117}\)
Chứng minh rằng:\(1-\dfrac{1}{2}+\dfrac{1}{3}-\dfrac{1}{4}+...+\dfrac{1}{121}-\dfrac{1}{122}+\dfrac{1}{123}=\dfrac{1}{62}+\dfrac{1}{63}+...+\dfrac{1}{122}+\dfrac{1}{123}\)
Tìm x :
\(\dfrac{1}{4}\) . \(\dfrac{2}{6}\) . \(\dfrac{3}{8}\) . \(\dfrac{4}{10}\) . .... . \(\dfrac{30}{62}\) . \(\dfrac{31}{64}\)
`1/4. 2/6. 3/8. 4/10........ 30/62. 31/64=2^x`
`=>\underbrace{1/2. 1/2. 1/2. 1/2..............1/2}_{\text{30 số 2}}. 1/64=2^x`
`=>(1/2)^{30}.(1/2)^{6}=2^x`
`=>(1/2)^{36}=2^x`
`=>2^{-36}=2^x`
`=>x=-36`
Vậy `x=-36`
Tìm x, biết \(\dfrac{1}{4}.\dfrac{2}{6}.\dfrac{3}{8}.\dfrac{4}{10}.\dfrac{5}{12}...\dfrac{30}{62}.\dfrac{31}{64}=2^x\)
=>\(1\cdot\dfrac{2}{4}\cdot\dfrac{3}{6}\cdot...\cdot\dfrac{31}{62}\cdot\dfrac{1}{64}=2^x\)
=>\(2^x=\dfrac{1}{2}\cdot\dfrac{1}{2}\cdot...\cdot\dfrac{1}{2}\cdot\dfrac{1}{64}=\left(\dfrac{1}{2}\right)^{30}\cdot\left(\dfrac{1}{2}\right)^6=\dfrac{1}{2^{36}}\)
=>x=-36
Tìm số nguyên n, biết rằng:
\(\dfrac{1}{4} . \dfrac{2}{6} . \dfrac{3}{8} .\dfrac{4}{10} . \dfrac{5}{12} .... \dfrac{30}{62} . \dfrac{31}{64} = 2^{n}\)\(\)
\(\dfrac{1}{2.2}.\dfrac{2}{2.3}.....\dfrac{31}{64}=2^x\\ =>\dfrac{1}{2.2.2.....2.64}=2^x\\ \dfrac{1}{2^{30}.26}=2^x\\ =>\dfrac{1}{2^{36}}=2^x\\ =>2^{-36}=2^x\\ =>x=-36\)
Ta có: \(2^n=\dfrac{1}{4}.\dfrac{2}{6}.\dfrac{3}{8}.\dfrac{4}{10}.\dfrac{5}{12}....\dfrac{30}{62}.\dfrac{31}{64}\)
⇔ \(2^n=\dfrac{1.2.3.4....31}{2.\left(2.3.4.....1\right).64}=\)
⇔ \(2^n=\dfrac{1}{2}.\dfrac{1}{64}=\dfrac{1}{128}\) \(\Leftrightarrow\) \(2^n=\dfrac{1}{2^6}\)
⇔ \(2^{x+6}=1\)
⇔ \(x+6=0\)
⇒ \(\left\{{}\begin{matrix}x=6\\x=-6\end{matrix}\right.\)
Câu 1: Tính giá trị biểu thức:
a.A=\(\left(\dfrac{136}{15}-\dfrac{28}{5}+\dfrac{62}{10}\right)\).\(\dfrac{21}{24}\)
b.B=\(\dfrac{5}{6}\)+6\(\dfrac{5}{6}\)\(\left(11\dfrac{5}{20}-9\dfrac{1}{4}\right)\):8\(\dfrac{1}{3}\)
c.C=1+3+6+10+15+...+1225.