1. Tính nhanh:
a, 1/1 * 2 + 1/2 * 3 + 1/3 * 4
b, 5/11 *16 + 5/16 * 21 + 5/21 * 26
c, 1/20 + 1/30 + 1/42
Tính :
a) C = -1/2 : -2/3 : -3/4
b) D = -6/5 : -5/4 : -4/3
c) 4/20 + 16/42 + 6/15 + -3/5 + 2/21 + -10/21 + 3/20
d)42/46 + 250/186 + -2121/2323 + -125125/143143
a: \(C=\dfrac{-1}{2}:\dfrac{-2}{3}:\dfrac{-3}{4}\)
\(=\dfrac{-1}{2}\cdot\dfrac{3}{-2}\cdot\dfrac{4}{-3}\)
\(=-\dfrac{4}{4}=-1\)
b: \(D=\dfrac{-6}{5}:\dfrac{-5}{4}:\dfrac{-4}{3}\)
\(=-\dfrac{6}{5}\cdot\dfrac{4}{5}\cdot\dfrac{3}{4}\)
\(=\dfrac{-18}{25}\)
c: \(\dfrac{4}{20}+\dfrac{16}{42}+\dfrac{6}{15}+\dfrac{-3}{5}+\dfrac{2}{21}+\dfrac{-10}{21}+\dfrac{3}{20}\)
\(=\left(\dfrac{4}{20}+\dfrac{-3}{5}+\dfrac{6}{15}\right)+\left(\dfrac{16}{42}+\dfrac{2}{21}-\dfrac{10}{21}\right)+\dfrac{3}{20}\)
\(=\left(\dfrac{1}{5}-\dfrac{3}{5}+\dfrac{2}{5}\right)+\left(\dfrac{8}{21}+\dfrac{2}{21}-\dfrac{10}{21}\right)+\dfrac{3}{20}\)
\(=\dfrac{3}{20}\)
d: \(\dfrac{42}{46}+\dfrac{250}{186}+\dfrac{-2121}{2323}+\dfrac{-125125}{143143}\)
\(=\dfrac{21}{23}+\dfrac{125}{93}+\dfrac{-21}{21}+\dfrac{-125}{143}\)
\(=\dfrac{125}{93}-\dfrac{125}{143}=\dfrac{6250}{13299}\)
Tính nhanh tổng:
a, S=1 - 1/5 +7/12 -9/20 + 11/30 - 13/42 + 15/56 + 19/90 - 21/110 + 23/132
b, P=21 * (4/1*3 - 8/3*5 + 12/5*7 - 16/7*9 + ... + 36/17*19 - 40/19*21 ( dấu * là dấu nhân nhé)
tính nhanh
a) 1/1*2 + 1/2*3 + 1/3*4 + 1/4*5 + ......... + 1/98*99 + 1/99*100
b) 5/11*16 + 5/16*21 + 5/21*16 + .......... + 5/61*66
a)\(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+...+\frac{1}{98.99}+\frac{1}{99.100}\)
\(=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+...+\frac{1}{99}-\frac{1}{100}\)
\(=1-\frac{1}{100}\)
\(=\frac{99}{100}\)
b)\(\frac{5}{11.16}+\frac{5}{16.21}+...+\frac{5}{61.66}\)
\(=\frac{1}{11}-\frac{1}{16}+\frac{1}{16}-\frac{1}{21}+....+\frac{1}{61}-\frac{1}{66}\)
\(=\frac{1}{11}-\frac{1}{66}\)
\(=\frac{5}{66}\)
a,\(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{98.99}+\frac{1}{99.100}\)
ta có:
\(\frac{1}{1.2}=\frac{2-1}{1.2}=\frac{2}{1.2}-\frac{1}{1.2}=1-\frac{1}{2}\)
\(\frac{1}{2.3}=\frac{3-2}{2.3}=\frac{3}{2.3}-\frac{2}{2.3}=\frac{1}{2}-\frac{1}{3}\)
...
\(\frac{1}{99.100}=\frac{1}{99}-\frac{1}{100}\)
= \(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{99}-\frac{1}{100}\)
=\(1-\frac{1}{100}=\frac{99}{100}\)
b,
\(\frac{5}{11.16}+\frac{5}{16.21}+\frac{5}{21.16}+...+\frac{5}{61.66}\)
ta có:
\(\frac{5}{11.16}=\frac{16-11}{11.16}=\frac{16}{11.16}-\frac{11}{11.16}=\frac{1}{11}-\frac{1}{16}\)
\(\frac{5}{16.21}=\frac{21-16}{16.21}=\frac{21}{16.21}-\frac{16}{16.21}=\frac{1}{16}-\frac{1}{21}\)
...
\(\frac{5}{61.66}=\frac{66-61}{61.66}=\frac{66}{61.66}-\frac{61}{61.66}=\frac{1}{61}-\frac{1}{66}\)
= \(\frac{1}{11}-\frac{1}{16}+\frac{1}{16}-\frac{1}{21}+...+\frac{1}{61}-\frac{1}{66}\)
=\(\frac{1}{11}-\frac{1}{66}\)=\(\frac{5}{66}\)
Bài 1: Tính nhanh
a, 5/11 + 1/2 + 2/5 + 6/11 + 3/4 + 16/25 + 5/16
b,19/4 + 37/100 + 1/8 + 132/25 + 5/2 + 37/12
c, 1313/1313 * 165165/143143 * 424242/151515
d, (121/122 * 123/125 + 127/129) * (1995/1996 * 17/16 - 21/25 : 16/17) * (42/30 * 75/23 - 19/23 * 210/38)
Tính nhanh:
a) -5/9 - 4/15 + 2/9 -11/15
b -8/13 - 7/16 + 21/13 - 1/6
c -15/25 - 14/21 + 8/5 - 5/3
giúp mình v chiều về m đi học r
a) \(\dfrac{-5}{9}-\dfrac{4}{15}+\dfrac{2}{9}-\dfrac{11}{15}\)
\(=\left(\dfrac{-5}{9}+\dfrac{2}{9}\right)-\left(\dfrac{4}{15}+\dfrac{11}{15}\right)\)
\(=\dfrac{-3}{9}-\dfrac{15}{15}\)
\(=-\dfrac{1}{3}-1\)
\(=-\dfrac{4}{3}\)
b) \(\dfrac{-8}{13}-\dfrac{7}{16}+\dfrac{21}{13}-\dfrac{1}{6}\)
\(=\left(\dfrac{-8}{13}+\dfrac{21}{13}\right)-\dfrac{7}{16}-\dfrac{1}{6}\)
\(=\dfrac{13}{13}-\dfrac{29}{48}\)
\(=1-\dfrac{29}{48}\)
\(=\dfrac{19}{48}\)
c) \(\dfrac{-15}{25}-\dfrac{14}{21}+\dfrac{8}{5}-\dfrac{5}{3}\)
\(=\dfrac{-3}{5}-\dfrac{2}{3}+\dfrac{8}{5}-\dfrac{5}{3}\)
\(=\left(\dfrac{-3}{5}+\dfrac{8}{5}\right)-\left(\dfrac{2}{3}+\dfrac{5}{3}\right)\)
\(=\dfrac{5}{5}-\dfrac{7}{3}\)
\(=1-\dfrac{7}{3}\)
\(=-\dfrac{4}{3}\)
a: =-5/9+2/9-11/15-4/15
=-3/9-1
=-12/9=-4/3
b: =-8/13+21/13-7/16-1/6
=1-1/6-7/16
=5/6-7/16
=19/48
c: =-15/25+8/5-2/3-5/3
=-7/3+1
=-4/3
a) \(-\dfrac{5}{9}-\dfrac{4}{15}+\dfrac{2}{9}-\dfrac{11}{15}\)
\(=\left(-\dfrac{5}{9}+\dfrac{2}{9}\right)+\left(-\dfrac{4}{15}-\dfrac{11}{15}\right)\)
\(=-\dfrac{1}{3}-1=-\dfrac{4}{3}\)
b) \(-\dfrac{8}{13}-\dfrac{7}{16}+\dfrac{21}{13}-\dfrac{1}{16}\)(sửa đề)
\(=\left(-\dfrac{8}{13}+\dfrac{21}{13}\right)+\left(-\dfrac{7}{16}-\dfrac{1}{16}\right)\)
\(=1-\dfrac{1}{2}=\dfrac{1}{2}\)
c) \(-\dfrac{15}{25}-\dfrac{14}{21}+\dfrac{8}{5}-\dfrac{5}{3}\)
\(=-\dfrac{3}{5}-\dfrac{2}{3}+\dfrac{8}{5}-\dfrac{5}{3}\)
\(=\left(-\dfrac{3}{5}+\dfrac{8}{5}\right)-\left(\dfrac{2}{3}+\dfrac{5}{3}\right)\)
\(=1-\dfrac{7}{3}=\dfrac{-4}{3}\)
tính
a/ 3 và 1/2 - 4/5 - 8 và 1/2 -1/5 -(2021)^0
b/ 32^5/ 16^5 - (0.2)^100 * (5)^100 -√8181 + /-21/
c/ 3/2* 16/21 + 3/2 * 5/21 - (- 1/10) ^0 - /-20/
c: \(=\dfrac{3}{2}\cdot1-1-20=\dfrac{3}{2}-21=\dfrac{-39}{2}\)
Tính nhanh:
a) 3/5 + 6/11 + 7/13 +2/5 + 16/11 + 19/13
b) 1/2 +1/6 + 1/12 + 1/20 + 1/30 + 1/42
\(\left(\frac{3}{5}+\frac{2}{5}\right)+\left(\frac{6}{11}+\frac{16}{11}\right)+\left(\frac{7}{13}+\frac{19}{13}\right)\)
= 1 + 2 + 2
= 5
\(=\frac{1}{1\cdot2}+\frac{1}{2\cdot3}+\frac{1}{3\cdot4}+\frac{1}{4\cdot5}+\frac{1}{5\cdot6}+\frac{1}{6\cdot7}\)
= \(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}\)
=\(1-\frac{1}{7}\)
=\(\frac{6}{7}\)
xin hiểu / là phần
a/ 3 và 1/2 - 4/5 - 8 và 1/2 -1/5 -(2021)^0
b 32^5/ 16^5 - (0.2)^100 * (5)^100 -√8181 + /-21/
c 3/2* 16/21 + 3/2 * 5/21 - (- 1/10) ^0 - /-20/
b: \(=2^5-1-9+21=53-10=43\)
xin hiểu / là phần
a/ 3 và 1/2 - 4/5 - 8 và 1/2 -1/5 -(2021)^0
b 32^5/ 16^5 - (0.2)^100 * (5)^100 -√8181 + /-21/
c 3/2* 16/21 + 3/2 * 5/21 - (- 1/10) ^0 - /-20/
c: \(=\dfrac{3}{2}-1-21=\dfrac{3}{2}-21=\dfrac{-39}{2}\)