Violympic toán 9
Các câu hỏi tương tự
cho số n nguyên dương và các tổng sau:
S_11+dfrac{1}{5}, S_21+dfrac{1}{5}+dfrac{1}{5^2}, S_31+dfrac{1}{5}+dfrac{1}{5^2}+dfrac{1}{5^3}, S_n1+dfrac{1}{5}+dfrac{1}{5^2}+dfrac{1}{5^3}+........+dfrac{1}{5^n}
Chứng minh rằng: dfrac{1}{5S_1^2}+dfrac{1}{5^2S_2^2}+dfrac{1}{5^3S^2_3}+.....+dfrac{1}{5^nS^2_n} dfrac{35}{36}
Đọc tiếp
cho số n nguyên dương và các tổng sau:
S\(_1\)=1+\(\dfrac{1}{5}\), S\(_2\)=1+\(\dfrac{1}{5}+\dfrac{1}{5^2}\), S\(_3\)=1+\(\dfrac{1}{5}+\dfrac{1}{5^2}+\dfrac{1}{5^3}\), S\(_n\)=1+\(\dfrac{1}{5}+\dfrac{1}{5^2}+\dfrac{1}{5^3}+........+\dfrac{1}{5^n}\)
Chứng minh rằng: \(\dfrac{1}{5S_1^2}+\dfrac{1}{5^2S_2^2}+\dfrac{1}{5^3S^2_3}+.....+\dfrac{1}{5^nS^2_n}< \dfrac{35}{36}\)
tính nhanh \(S=2^{100}-2^{99}+2^{98}+..+2^2-2\)
\(\left(100+\dfrac{99}{2}+\dfrac{98}{3}+\dfrac{97}{4}....+\dfrac{1}{100}\right):\left(\dfrac{1}{2}+\dfrac{1}{3}+\dfrac{1}{4}+....\dfrac{1}{100}\right)-2\)
Tính tổng sau:
S=\(\frac{1}{2\sqrt[]{1}+1\sqrt[]{2}}+\frac{1}{3\sqrt[]{2}+2\sqrt[]{3}}+.........+\frac{1}{100\sqrt[]{99}+99\sqrt[]{100}}\)
Tính các tích sau:
P_1 left(1+dfrac{2}{4}right)left(1+dfrac{2}{10}right)left(1+dfrac{2}{18}right)....left(1+dfrac{2}{n^2+3n}right)
P_2 left(1+dfrac{1}{3}right)left(1+dfrac{1}{8}right)left(1+dfrac{1}{15}right)....left(1+dfrac{2}{n^2+2n}right)
P_3 left(1-dfrac{1}{1+2}right)left(1-dfrac{1}{1+2+3}right)left(1-dfrac{1}{1+2+3+4}right).....left(1-dfrac{1}{1+2+3+4+...+n}right)
P_4 dfrac{2^4+4}{4^4+4}.dfrac{6^4+4}{8^4+4}.dfrac{8^4+4}{10^4+4}....dfrac{18^4+4}{20^4+4}
Đọc tiếp
Tính các tích sau:
P\(_1\) =\(\left(1+\dfrac{2}{4}\right)\left(1+\dfrac{2}{10}\right)\left(1+\dfrac{2}{18}\right)....\left(1+\dfrac{2}{n^2+3n}\right)\)
P\(_2\) =\(\left(1+\dfrac{1}{3}\right)\left(1+\dfrac{1}{8}\right)\left(1+\dfrac{1}{15}\right)....\left(1+\dfrac{2}{n^2+2n}\right)\)
P\(_3\) = \(\left(1-\dfrac{1}{1+2}\right)\left(1-\dfrac{1}{1+2+3}\right)\left(1-\dfrac{1}{1+2+3+4}\right).....\left(1-\dfrac{1}{1+2+3+4+...+n}\right)\)
P\(_4\) = \(\dfrac{2^4+4}{4^4+4}.\dfrac{6^4+4}{8^4+4}.\dfrac{8^4+4}{10^4+4}....\dfrac{18^4+4}{20^4+4}\)
So sánh A với 1
\(A=\dfrac{1}{2\sqrt{1}+1\sqrt{2}}+\dfrac{1}{3\sqrt{2}+2\sqrt{3}}+\dfrac{1}{4\sqrt{3}+3\sqrt{4}}+...+\dfrac{1}{100\sqrt{99}+99\sqrt{100}}\)
Tính các tổng sau:
\(T=\dfrac{1}{1+\sqrt{5}}+\dfrac{1}{\sqrt{5}+\sqrt{9}}+\dfrac{1}{\sqrt{9}+\sqrt{13}+......+\dfrac{1}{\sqrt{2013}+\sqrt{2017}}}\)
\(S=\dfrac{1}{2\sqrt{1}+1\sqrt{2}}+\dfrac{1}{3\sqrt{2}+2\sqrt{3}}+.....+\dfrac{1}{100\sqrt{99}+99\sqrt{100}}\)
tính (100+ 99/2 +98/3 +...+ 1/100) / (1/2 + 1/3 +1/4+...+ 1/101) -2
chung minh S chia het cho 40 biet \(S=1+3+3^2+3^3+...+3^{98}+3^{99}\)