1/100.(100/1.101+2.202+...+100/25.125)
Cho
\(A=\dfrac{1}{1.101}+\dfrac{1}{2.102}+\dfrac{1}{3.103}+...+\dfrac{1}{25.125}\)
\(B=\dfrac{1}{1.26}+\dfrac{1}{2.27}+\dfrac{1}{3.28}+...+\dfrac{1}{100.125}\)
Trong đó A có 25 số hạng,B có 100 số hạng.Tìm thương A:B
Gọi x là thương A:B cần tìm.Theo đề, ta có:
\(\left(\dfrac{1}{1.26}+\dfrac{1}{2.27}+...+\dfrac{1}{100.125}\right)x=\dfrac{1}{1.101}+\dfrac{1}{2.102}+...+\dfrac{1}{25.125}\)
Nhân 2 vế cho 100, ta có:
\(4\left(\dfrac{25}{1.26}+\dfrac{25}{2.27}+...+\dfrac{25}{100.125}\right)x=\dfrac{100}{1.101}+\dfrac{100}{2.102}+...+\dfrac{100}{25.125}\)
\(\Rightarrow4\left(1-\dfrac{1}{26}+\dfrac{1}{2}-\dfrac{1}{27}+...+\dfrac{1}{100}-\dfrac{1}{125}\right)x=1-\dfrac{1}{101}+\dfrac{1}{2}-\dfrac{1}{102}+...+\dfrac{1}{25}-\dfrac{1}{125}\)
\(\Rightarrow4\left[\left(1+\dfrac{1}{2}+...+\dfrac{1}{100}\right)-\left(\dfrac{1}{26}+\dfrac{1}{27}+...+\dfrac{1}{125}\right)\right]x=\left(1+\dfrac{1}{2}+...+\dfrac{1}{25}\right)-\left(\dfrac{1}{101}+\dfrac{1}{102}+...+\dfrac{1}{125}\right)\)\(\Rightarrow4x=1\Rightarrow x=\dfrac{1}{4}\)
Vậy hiệu A:B là:\(\dfrac{1}{4}\)
( 1 / 1.101 + 1 / 2.102 + 1 / 3.103 + ... + 1 / 10.110 ) . x = 1 / 1.11 + 1 / 2.12 + ... + 1 / 100 . 110
Bài 1:\(\left(\frac{1}{1.101}+\frac{1}{2.202}+\frac{1}{3.303}+...+\frac{1}{10.10}\right).x=\frac{1}{1.11}+\frac{1}{2.12}+...+\frac{1}{100.10}\)
Tìm x
Cho A =\(\frac{1}{1.101}\) + \(\frac{1}{2.102}\) + \(\frac{1}{3.103}\) + ...... + \(\frac{1}{25.125}\)
B =\(\frac{1}{1.26}\) + \(\frac{1}{2.27}\) + \(\frac{1}{3.28}\) + ....... + \(\frac{1}{100.125}\)
A có 25 số hạng, B có 100 số hạng . Tìm thương A : B
1. Cho A=\(\frac{1}{1.101}\)+\(\frac{1}{2.102}\)+...+\(\frac{1}{10.110}\); B= \(\frac{1}{1.11}\)+\(\frac{1}{2.12}\)+...+\(\frac{1}{100.110}\)
Tính A : B
2. Cho A= 1+\(\frac{3}{2^3}\)+\(\frac{4}{2^4}\)+...+\(\frac{100}{2^{100}}\).Rút gọn A
So sánh bt: \(M=\dfrac{100^{100}+1}{100^{99}+1};N=\dfrac{100^{101}+1}{100^{100}+1}\)
Ta có:
\(M=\dfrac{100^{100}+1}{100^{99}+1}\)
\(\Rightarrow\dfrac{M}{100}=\dfrac{100^{100}+1}{100\cdot\left(100^{99}+1\right)}\)
\(\Rightarrow\dfrac{M}{100}=\dfrac{100^{100}+1}{100^{100}+100}\)
\(\Rightarrow\dfrac{M}{100}=1-\dfrac{99}{100^{100}+100}\)
\(N=\dfrac{100^{101}+1}{100^{100}+1}\)
\(\Rightarrow\dfrac{N}{100}=\dfrac{100^{101}+1}{100\cdot\left(100^{100}+1\right)}\)
\(\Rightarrow\dfrac{N}{100}=\dfrac{100^{101}+1}{100^{101}+100}\)
\(\Rightarrow\dfrac{N}{100}=1-\dfrac{99}{100^{101}+100}\)
Mà: \(100^{101}>100^{100}\)
\(\Rightarrow100^{101}+100>100^{100}+100\)
\(\Rightarrow\dfrac{99}{100^{101}+100}< \dfrac{99}{100^{100}+100}\)
\(\Rightarrow1-\dfrac{99}{101^{101}+100}< 1-\dfrac{99}{100^{100}+100}\)
\(\Rightarrow\dfrac{N}{100}< \dfrac{M}{100}\)
\(\Rightarrow N< M\)
(1^100+2^100+...+10^100):(1^100+2^100+...+10^100)
Tính
A=1.(100-1)+2.(100-2)+3.(100-3)+..............+99.(100-99)
B=1.(100+1)+2.(100+2)+3.(100+3)+...........+99.(100+99)
so sanh A va B
A = 100^101 + 1 / 100^100 + 1
B = 100^100 + 1 / 100^99 + 1
A=100^101+1/100^100+1
B=100^100+1/100^99+1
A<100^101+1+99/100^100+1+99
A<100^101+100/100^100+100
A<100.(100^100+1)/100.(100^99+1)
A<100^100+1/100^99+1=B
=> A<B
Vậy A<B