tính E=1/56+1/140+1/260+..+1/1400
Tính B=1-10/56-10/140-10/260-...-10/1400
Cho hai biểu thức D và E như sau:
D = 10/56 + 10/140 + 10/260 + ...+ 10/1400 ;
E = 1/1+2 + 1/1+2+3 + 1/1+2+3+4 +...+ 1/1+2+3+...+24
tính tỉ số D/E
1, Tính tổng
A= 10/56 + 10/140 + 10/260 +....+ 10/1400
@py. Hello, hihi
Đề Bài: Tính:
a) B bằng 1/6+ 1/12+ 1/20+ 1/42+ 1/56+ 1/72+ 1/90
b) C bằng 10/56+ 10/140+ 10/260+...+ 10/1400
D = 10/56 + 10/140 + 10/260 + ... + 10/1400
E =1/1+2 + 1/ 1+2+3 + 1/1+2+3+4 + .....+ 1/1+2+3+4+....+24
tính tỉ số giữa D và E
Sorry đăng làm giwor thì em nó bấm nộp bài mk làm tiếp nhé
\(E=\frac{1}{1+2}+\frac{1}{1+2+3}+\frac{1}{1+2+3+4}+......+\frac{1}{1+2+3+.....+24}\)
\(=\frac{1}{\frac{\left(2-1\right).2}{2}}+\frac{1}{\frac{\left(3-1\right).3}{2}}+.....+\frac{1}{\frac{\left(24-1\right).24}{2}}\)
\(=\frac{1}{\frac{1.2}{2}}+\frac{1}{\frac{2.3}{2}}+\frac{1}{\frac{3.4}{2}}+.....+\frac{1}{\frac{23.24}{2}}\)
\(=\frac{2}{1.2}+\frac{2}{2.3}+\frac{2}{3.4}+.....+\frac{2}{23.24}\)
\(=2\left(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+.....+\frac{1}{23.24}\right)\)
\(=2.\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+.....+\frac{1}{23}-\frac{1}{24}\right)\)
\(=2\left(1-\frac{1}{24}\right)\)
\(=2.\frac{23}{24}=\frac{23}{12}\)
Vậy tỉ số giữa D và E là ; \(\frac{5}{28}:\frac{23}{2}=\frac{5}{322}\)
Ta có : \(D=\frac{10}{56}+\frac{10}{140}+\frac{10}{260}+.....+\frac{10}{1400}\)
\(=\frac{5}{4.7}+\frac{5}{7.10}+\frac{5}{10.13}+.....+\frac{5}{25.28}\)
\(=\frac{5}{3}.\left(\frac{3}{4.7}+\frac{3}{7.10}+\frac{3}{10.13}+.....+\frac{3}{25.28}\right)\)
\(=\frac{5}{3}\left(\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+.....+\frac{1}{25}-\frac{1}{28}\right)\)
\(=\frac{5}{3}.\left(\frac{1}{4}-\frac{1}{7}\right)\)
\(=\frac{5}{3}.\frac{3}{28}=\frac{5}{28}\)
\(D=\frac{10}{56}+\frac{10}{140}+\frac{10}{260}+...+\frac{10}{1400}\)
\(E=\frac{1}{1+2}+\frac{1}{1+2+3}+...+\frac{1}{1+2+3+...+24}\)
Tính tỉ số\(\frac{D}{E}\)
Tính nhanh
a)A = 1 + 1/2 +1/4 + .......+ 1/2^99 +1/2^100+1/2^100
b) 12/56 + 12/140+12/260 +.....+ 12/1400
Tính nhanh nha
E=10/56 + 10/140 + 10/260 +...+10/1400
E=10/56 + 10/140 + 10/260 +...+10/1400
E=5/28+5/70+5/130+...+5/700
3E/5=3/4.7+3/7.10+3/10.13+...+3/25.28
3E/5=1/4-1/7+1/7-1/10+1/10-1/13+...+1/25-1/28
3E/5=1/4-1/28
3E/5=3/14
E=3/14.5/3
E=5/14
Vậy E=5/14
cho A=-10/56+-10/140+-10/260+......................+-10/1400. so sánh A với B=-1/3