\(B=\frac{1}{3}+\frac{1}{3^2}+\frac{1}{3^3}+......+\frac{1}{3^{100}}\Rightarrow3B=1+\frac{1}{3}+\frac{1}{3^2}+.........+\frac{1}{3^{99}}\Rightarrow3B-B=2B=\left(1+\frac{1}{3}+\frac{1}{3^2}+.....+\frac{1}{3^{99}}\right)-\left(\frac{1}{3}+\frac{1}{3^2}+....+\frac{1}{3^{99}}\right)=1-\frac{1}{3^{99}}\Rightarrow B=\frac{3^{99}-1}{2.3^{99}}\)
Tính tổng sau
1) B= 1.2+2.3+3.4+......+99.100
2) C= \(1^2+2^2+3^2+...+99^2\)
3) D= \(\left(1-\frac{1}{2^2}\right)\left(1-\frac{1}{3^2}\right)\left(1-\frac{1}{4^2}\right).....\left(1-\frac{1}{n^2}\right)\)
4) E=\(\frac{1}{3^2}+\frac{1}{3^3}+\frac{1}{3^4}+....+\frac{1}{3^{100}}\)
CMR:
a) \(\frac{1}{2!}+\frac{2}{3!}+\frac{3}{4!}+...+\frac{99}{100!}< 1\)
b) \(\frac{1.2-1}{2!}+\frac{2.3-1}{3!}+\frac{3.4-1}{4!}+...+\frac{99.100-1}{100!}< 2\)
a) CM: A2= \(\frac{1}{\sqrt{1}}+\frac{1}{\sqrt{2}}+\frac{1}{\sqrt{3}}+\frac{1}{\sqrt{4}}+...+\frac{1}{\sqrt{100}}>10\)
b) CM: A3= \(\frac{1}{2!}+\frac{2}{3!}+\frac{3}{4!}+\frac{4}{5!}+...+\frac{99}{100!}< 1\)
Chứng minh: \(\frac{1}{3}+\frac{2}{3^2}+\frac{3}{3^3}+\frac{4}{3^4}+...................+\frac{100}{3^{100}}< \frac{3}{4}\)
Chứng minh: \(\frac{1}{3}+\frac{2}{3^2}+\frac{3}{3^3}+\frac{4}{3^4}+...................+\frac{100}{3^{100}}< \frac{3}{4}\)
Chứng minh rằng: \(\frac{1}{3}+\frac{2}{3^2}+\frac{3}{3^3}+\frac{4}{3^4}+....................+\frac{100}{3^{100}}< \frac{3}{4}\)
cho biểu thức: \(A=\left(\frac{-1}{3}\right)+\frac{1}{3^2}-\frac{1}{3^3}+...+\frac{1}{3^{100}}\)
tính \(B=4\left|A\right|+\frac{1}{3^{100}}\)
tính giá trị biểu thức
A=\(\frac{\left[1+2+3+......+100\right].\left[\frac{1}{2}-\frac{1}{3}-\frac{1}{4}-\frac{1}{5}\right].\left[2,4.42-21.4,8\right]}{1+\frac{1}{2}+\frac{1}{3}+\frac{1}{4}+....+\frac{1}{100}}\)
tính
a)\(\left(1-\frac{1}{1+2}\right).\left(1-\frac{1}{1+2+3}\right).\left(1-\frac{1}{1+2+3+4}\right).....\left(1-\frac{1}{1+2+3+...+20}\right)\)
b)\(\frac{\left(1+2+3+...+100\right).\left(12.3,4-6,86\right)}{\frac{1}{2}+\frac{1}{3}+\frac{1}{4}+\frac{1}{5}+\frac{1}{6}}\)
c)(18.123+9.436.2+3.5310.6):1+4+7+...+100-410)
giúp mk vs mai mk kiểm tra rồi . ai đúng mk tick nha
