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1:99 phần 100 : 98 phần 99 : 97 phần 98 : ... : 2 phần 3 : 1 phần 2
Ai giải nhanh được 2 thích
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`A=1/(1xx2)+1/(2xx3)+1/(3xx4)+...+1/(99xx100)`
`=> A=(2-1)/(1xx2)+(3-2)/(2xx3)+...+(100-99)/(99xx100)`
`=> A=1-1/2+1/2-1/3+...+1/99-1/100`
`=> A=1-1/100`
`=> A=99/100
Sửa đề:
A = 1/(1.2) + 1/(2.3) + 1/(3.4) + ... + 1/(97.98) + 1/(98.99) + 1/(99.100)
= 1 - 1/2 + 1/2 - 1/3 + 1/3 - 1/4 + ... + 1/97 - 1/98 + 1/98 - 1/99 + 1/99 - 1/100
= 1 - 1/100
= 99/100
a
\(A=1+3+3^2+3^3+....+3^{100}\)
\(3A=3+3^2+3^3+3^4+.....+3^{101}\)
\(2A=3^{101}-1\)
\(A=\frac{3^{101}-1}{2}\)
b
\(B=\frac{1}{2}+\frac{1}{2^2}+\frac{1}{2^3}+....+\frac{1}{2^{99}}\)
\(2B=1+\frac{1}{2}+\frac{1}{2^2}+...+\frac{1}{2^{98}}\)
\(B=1-\frac{1}{2^{99}}\)
c
\(C=5^{100}-5^{99}+5^{98}-5^{97}+....+5^2-5+1\)
\(5C=5^{101}-5^{100}+5^{99}-5^{98}+....+5^3-5^2+5\)
\(6C=5^{101}+1\)
\(C=\frac{5^{101}+1}{6}\)
\(B=\frac{1}{2}+\left(\frac{1}{2}\right)^2+\left(\frac{1}{2}\right)^3+...+\left(\frac{1}{2}\right)^{99}\)
\(\Rightarrow\frac{1}{2}B=\)\(\left(\frac{1}{2}\right)^2+\left(\frac{1}{2}\right)^3+...+\left(\frac{1}{2}\right)^{100}\)
\(\Rightarrow B-\frac{1}{2}B=\left[\left(\frac{1}{2}\right)^2+\left(\frac{1}{2}\right)^3+...+\left(\frac{1}{2}\right)^{99}\right]-\left[\left(\frac{1}{2}\right)+\left(\frac{1}{2}\right)^2+...+\left(\frac{1}{2}\right)^{100}\right]\)
\(\Rightarrow\frac{1}{2}B=\frac{1}{2}-\left(\frac{1}{2}\right)^{100}\Rightarrow B=\left[\frac{1}{2}-\left(\frac{1}{2}\right)^{100}\right].2\)
Bài 1:
a: \(2P=2^{101}-2^{100}+2^{98}-2^{97}+...+2^3-2^2\)
=>\(3P=2^{101}-2\)
hay \(P=\dfrac{2^{101}-2}{3}\)
b: \(5Q=5^{101}-5^{100}+5^{99}-5^{98}+...+5^3-5^2+5\)
=>\(6Q=5^{101}+1\)
hay \(Q=\dfrac{5^{101}+1}{6}\)
#muon roi ma sao con
\(\frac{x+1}{99}+\frac{x+2}{98}+\frac{x+3}{97}+\frac{x+4}{96}=-4\)
\(\Leftrightarrow\frac{x+100}{99}+\frac{x+100}{98}+\frac{x+100}{97}+\frac{x+100}{96}=0\)
\(\Leftrightarrow\left(x+100\right)\left(\frac{1}{99}+\frac{1}{98}+\frac{1}{97}+\frac{1}{96}\ne0\right)=0\Leftrightarrow x=-100\)
Vậy x = -100