tính
A=1.1/1.2.2.2/2.3.3.3/3.4....20.20/20.21
B=2^2/1.3.3^2/2.4.4^2/3.5...10^2/9.11
Những câu hỏi liên quan
Rút gọn biểu thức: A=2^2/1.3.3^2/2.4.4^2/3.5.5^2/4.6.....99^2/98.100
Ta có: \(A=\frac{2^2}{1.3}.\frac{3^2}{2.4}.\frac{4^2}{3.5}.....\frac{99^2}{98.100}\)
\(A=\frac{\left(2.3.4.5.....99\right).\left(2.3.4.5.....99\right)}{\left(1.2.3.4.....98\right).\left(3.4.5.6.....100\right)}\)
\(A=\frac{99.2}{100}=\frac{99}{50}\)
Học tốt!!!!
A= 1^2/1.2.2^2/2.3.3^2/3.4.4^2/4.5.5^2/5.6
B= 2^2/1.3.3^2/2.4.4^2/3.5.5^2/4.6
Giup minh nhe minh tick cho
A=12/1.2 . 22/2.3 . 32/3.4 . 42/4.5 . 52/5.6
⇒1.1/1.2 . 2.2/2.3 . 3.3/3.4 . 4.4/4.5 . 5.5/5.6
⇒1.2.3.4.5/1.2.3.4.5 . 1.2.3.4.5/2.3.4.5.6
⇒1 . 1/6 =1/6.
Vậy A=1/6
B=22/1.3 . 32/2.4 . 42/3.5 . 52/4.6
⇒2.2/1.3 . 3.3/2.4 . 4.4/3.5 . 5.5/4.6
⇒2.2.3.3.4.4.5.5/1.3.2.4.3.5.4.6 =48.
Vậy B=48.
Đúng 0
Bình luận (0)
Tính hợp lí
A=2^2/1.3.3^2/2.4+4^2/3.5. ... .999^2/998.1000
A = (2.3.4. .... .999/1.2.3. .... .998) . (2.3.4. .... .999/3.4.5. ..... .1000)
= 999. 2/1000
= 999/500
Tk mk nha
Đúng 0
Bình luận (0)
1) Tính 2/3.5+2/5.7+2/7.9+2/9.11+2/11.13+2/13.15+2/1.2+2/2.3+2/3.4+2/4.5+...+2/9.10
2) Tìm x biết: (11/12+11/12.24+11/23.34+...+11/89.100)
1)
2/3.5+2/5.7+...+2/11.13+2/13.15+2/1.2+2/2.3+...+2/9.10
=(2/3.5+...2/13.15)+(2/1.2+...+2/9.10)
= (2/3-2/15)+ [2(1-1/10)]
=8/15+9/5
=7/3
2)
11/12+11/12.24+...+11/88.99
=11-1/9
=10/8/9
Đúng 0
Bình luận (0)
text{Tìm x, biết:}a) x-dfrac{2}{3.5}-dfrac{2}{5.7}-dfrac{2}{7.9}-dfrac{2}{9.11}-dfrac{2}{11.13}-dfrac{2}{13.15}dfrac{2}{5}b) dfrac{1}{2.3}.x+dfrac{1}{3.4}.x+dfrac{1}{4.5}.x+...+dfrac{1}{49.50}.x1c) x-dfrac{20}{11.3}-dfrac{20}{13.15}-...-dfrac{53}{55}dfrac{3}{11}d) x+dfrac{4}{5.9}+dfrac{4}{9.13}+...+dfrac{4}{41.45}dfrac{-37}{45}e) left(dfrac{11}{12}.dfrac{11}{2.23}.dfrac{11}{23.34}...dfrac{11}{89.100}right).xdfrac{5}{3}f) left(dfrac{2}{11.13}.dfrac{2}{13.15}.dfrac{2}{15.17}...dfrac{2}{19.21}right...
Đọc tiếp
\(\text{Tìm x, biết:}\)
\(a\)) \(x-\dfrac{2}{3.5}-\dfrac{2}{5.7}-\dfrac{2}{7.9}-\dfrac{2}{9.11}-\dfrac{2}{11.13}-\dfrac{2}{13.15}=\dfrac{2}{5}\)
\(b\)) \(\dfrac{1}{2.3}.x+\dfrac{1}{3.4}.x+\dfrac{1}{4.5}.x+...+\dfrac{1}{49.50}.x=1\)
\(c\)) \(x-\dfrac{20}{11.3}-\dfrac{20}{13.15}-...-\dfrac{53}{55}=\dfrac{3}{11}\)
\(d\)) \(x+\dfrac{4}{5.9}+\dfrac{4}{9.13}+...+\dfrac{4}{41.45}=\dfrac{-37}{45}\)
\(e\)) \(\left(\dfrac{11}{12}.\dfrac{11}{2.23}.\dfrac{11}{23.34}...\dfrac{11}{89.100}\right).x=\dfrac{5}{3}\)
\(f\)) \(\left(\dfrac{2}{11.13}.\dfrac{2}{13.15}.\dfrac{2}{15.17}...\dfrac{2}{19.21}\right)-x+4+\dfrac{221}{231}=\dfrac{7}{3}\)
d) Ta có: \(x+\dfrac{4}{5\cdot9}+\dfrac{4}{9\cdot13}+...+\dfrac{4}{41\cdot45}=\dfrac{-37}{45}\)
\(\Leftrightarrow x+\dfrac{1}{5}-\dfrac{1}{9}+\dfrac{1}{9}-\dfrac{1}{13}+...+\dfrac{1}{41}-\dfrac{1}{45}=\dfrac{-37}{45}\)
\(\Leftrightarrow x+\dfrac{1}{5}-\dfrac{1}{45}=\dfrac{-37}{45}\)
\(\Leftrightarrow x=\dfrac{-37}{45}+\dfrac{1}{45}-\dfrac{1}{5}=\dfrac{-36}{45}-\dfrac{1}{5}=\dfrac{-4}{5}-\dfrac{1}{5}=-1\)
Vậy: x=-1
Đúng 1
Bình luận (0)
Tính hợp lí
A=2^2/1.3.3^2/2.4+4^2/3.5. ... .999^2/998.1000
\(A=\dfrac{2^2}{1\cdot3}\cdot\dfrac{3^2}{2\cdot4}\cdot\dfrac{4^2}{3\cdot5}\cdot...\cdot\dfrac{999^2}{998\cdot1000}\\ =\dfrac{2^2\cdot3^2\cdot4^2\cdot...\cdot999^2}{1\cdot3\cdot2\cdot4\cdot3\cdot5\cdot...\cdot998\cdot1000}\\ =\dfrac{\left(2\cdot3\cdot4\cdot...\cdot999\right)\cdot\left(2\cdot3\cdot4\cdot...\cdot999\right)}{\left(1\cdot2\cdot3\cdot...\cdot998\right)\cdot\left(3\cdot4\cdot5\cdot...\cdot1000\right)}\\ =\dfrac{2\cdot3\cdot4\cdot...\cdot999}{1\cdot2\cdot3\cdot...\cdot998}\cdot\dfrac{2\cdot3\cdot4\cdot...\cdot999}{3\cdot4\cdot5\cdot...\cdot1000}\\ =999\cdot\dfrac{1}{500}\\ =\dfrac{999}{500}\)
Đúng 0
Bình luận (0)
B=22/1.2.32/2.4.42/3.5...502/49.51
tính tổng S=2/1.3+2/3.5+2/5.7+2/7.9+2/9.11
\(S=\dfrac{2}{1\times3}+\dfrac{2}{3\times5}+\dfrac{2}{5\times7}+\dfrac{2}{7\times9}+\dfrac{2}{9\times11}\)
\(=\dfrac{1}{1}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{9}+\dfrac{1}{9}-\dfrac{1}{11}\)
\(=\dfrac{1}{1}-\dfrac{1}{11}=\dfrac{11}{11}-\dfrac{1}{11}=\dfrac{10}{11}\)
Đúng 1
Bình luận (0)
Tính giá trị biểu thức:
\(B=\frac{2^2}{1.3}.\frac{3^2}{2.4}.\frac{4^2}{3.5}...\frac{10^2}{9.11}\)
\(B=\frac{2^2}{1.3}.\frac{3^2}{2.4}.\frac{4^2}{3.5}......\frac{10^2}{9.11}=\frac{\left(1.2.3.....10\right)^2}{\left(1.2.3.....9\right).\left(3.4.5....9.10.11\right)}=\frac{\left(1.2.3....10\right)^2}{\left(1.2\right)\left(3.4.5.....9\right)^2\left(10.11\right)}=\frac{\left(1.2.10\right)^2}{\left(1.2\right).\left(10.11\right)}=\frac{1.2.10}{11}=\frac{20}{11}\)
Đúng 0
Bình luận (0)