tinh nhanh (1/21+1/210,+1/2010)*(1/3- 1/30-1/5-1/10)
Tính nhanh:\((\) \(\dfrac{1}{3}\)-\(\dfrac{1}{5}\)-\(\dfrac{1}{10}\)-\(\dfrac{1}{30}\))x(\(\dfrac{1}{21}\)+\(\dfrac{1}{210}\)+\(\dfrac{1}{2010}\))
\(=\left(\dfrac{1}{21}+\dfrac{1}{210}+\dfrac{1}{2010}\right)\cdot\dfrac{10-6-3-1}{30}=0\)
\(\left(\dfrac{1}{3}-\dfrac{1}{5}-\dfrac{1}{10}-\dfrac{1}{30}\right)\times\left(\dfrac{1}{21}+\dfrac{1}{210}+\dfrac{1}{2010}\right)\)
\(=\left(\dfrac{10}{30}-\dfrac{6}{30}-\dfrac{3}{30}-\dfrac{1}{30}\right)\times\left(\dfrac{1}{21}+\dfrac{1}{210}+\dfrac{1}{2010}\right)\)
\(=0\times\left(\dfrac{1}{21}+\dfrac{1}{210}+\dfrac{1}{2010}\right)\)
\(=0\)
(\(\frac{1}{21}+\frac{1}{210}+\frac{1}{2010}\))(\(\frac{1}{3}-\frac{1}{30}-\frac{1}{5}-\frac{1}{10}\))
Ta thấy: \(\frac{1}{3}\)- \(\frac{1}{30}\)- \(\frac{1}{5}\)- \(\frac{1}{10}\)
= \(\frac{10}{30}\)- \(\frac{1}{30}\)- \(\frac{6}{30}\)- \(\frac{3}{30}\)= 0
nên gtbt trên bằng 0
Tính nhanh ( 1/21 + 1/210 + 1/2010 ) x ( 1/4 - 1/40 - 1/8 - 1/10
(\(\frac{1}{21}\)+\(\frac{1}{210}\)+\(\frac{1}{2010}\))*(\(\frac{1}{3}\)-\(\frac{1}{30}\)-\(\frac{1}{5}\)-\(\frac{1}{10}\))
Ta có:
\(\left(\frac{1}{21}+\frac{1}{210}+\frac{1}{2010}\right)\)\(\times\)\(\left(\frac{1}{3}-\frac{1}{30}-\frac{1}{5}-\frac{1}{10}\right)\)
= \(\left(\frac{1}{21}+\frac{1}{210}+\frac{1}{2010}\right)\)\(\times\)\(\left(\frac{10}{30}-\frac{1}{30}-\frac{6}{30}-\frac{3}{30}\right)\)
= \(\left(\frac{1}{21}+\frac{1}{210}+\frac{1}{2010}\right)\)\(\times\)\(\left(\frac{10-1-6-3}{30}\right)\)
= \(\left(\frac{1}{21}+\frac{1}{210}+\frac{1}{2010}\right)\)\(\times\)\(0\)
= \(0\)
ta có \(\frac{1}{3}-\frac{1}{30}-\frac{1}{5}-\frac{1}{10}=\frac{10-1-6-3}{30}=\frac{0}{30}=0\)
=>\(\left(\frac{1}{21}+\frac{1}{210}+\frac{1}{2010}\right)x\left(\frac{1}{3}-\frac{1}{30}-\frac{1}{5}-\frac{1}{10}\right)=0\)
\(\left(\frac{1}{21}+\frac{1}{210}+\frac{1}{2010}\right)\times\left(\frac{1}{3}-\frac{1}{30}-\frac{1}{5}-\frac{1}{10}\right)\)
\(=\left(\frac{1}{21}+\frac{1}{210}+\frac{1}{2010}\right)\times\left(\frac{10}{30}-\frac{1}{30}-\frac{6}{30}-\frac{3}{30}\right)\)
\(=\left(\frac{1}{21}+\frac{1}{210}+\frac{1}{2010}\right)\times\left(\frac{10-1-6-3}{30}\right)\)
\(=\left(\frac{1}{21}+\frac{1}{210}+\frac{1}{2010}\right)\times\frac{0}{30}\)
\(=\left(\frac{1}{21}+\frac{1}{210}+\frac{1}{2010}\right)\times0\)
\(=0\)
Tính nhanh (nếu được)
3 x 15 + 21 x 15 + 85 x 5
15 - 30 + 40
21 + 19 - 50 + 10
1/5 - 1/4 + 2
(1/4 +1/6) x (1/2 -1/4)
1/10 + 1/5 - 3/4
3 x 15 + 21 x 15 + 85 x 5
= 45 + 315 + 425
= 785
15 - 30 + 40
= 25
21 + 19 - 50 + 10
= 0
\(\dfrac{1}{5}-\dfrac{1}{4}+2\)
\(=-\dfrac{1}{20}+2\)
\(=\dfrac{39}{20}\)
\(\left(\dfrac{1}{4}+\dfrac{1}{6}\right)\times\left(\dfrac{1}{2}-\dfrac{1}{4}\right)\)
\(=\dfrac{5}{12}\times\dfrac{1}{4}\)
\(=\dfrac{5}{12}\times\dfrac{3}{12}\)
\(=\dfrac{5}{48}\)
\(\dfrac{1}{10}+\dfrac{1}{5}-\dfrac{3}{4}\)
\(=-\dfrac{9}{20}\)
\(3\times15+21\times15+85\times5\\ =15\times\left(3+21\right)+425\\ =15\times24+425\\ =360+425\\ =785\)
\(15-30+40\\ =\left(15+40\right)-30\\ =55-30\\ =25\)
\(21+19-50+10\\ =\left(21+19\right)-\left(50-10\right)\\ =40-40\\ =0\)
\(\dfrac{1}{5}-\dfrac{1}{4}+2\)
\(=\dfrac{4}{20}-\dfrac{5}{20}+\dfrac{40}{20}\)
\(=\dfrac{\left(4+40\right)}{20}-\dfrac{5}{20}\)
\(=\dfrac{44}{20}-\dfrac{5}{20}\)
\(=\dfrac{39}{20}\)
\(\left(\dfrac{1}{4}+\dfrac{1}{6}\right)\times\left(\dfrac{1}{2}-\dfrac{1}{4}\right)\)
\(=\dfrac{5}{12}\times\dfrac{1}{4}\)
\(=\dfrac{5}{48}\)
\(\dfrac{1}{10}+\dfrac{1}{5}-\dfrac{3}{4}\)
\(=\dfrac{2}{20}+\dfrac{4}{20}-\dfrac{15}{20}\)
\(=\dfrac{6}{20}-\dfrac{15}{20}\)
\(=-\dfrac{9}{20}\)
Giúp tớ giải nốt 2 bài tính nhanh này nhé, thanks
B = 1/3 + 1/6 + 1/10 + 1/15 + 1/21 + 1/28
D = 2009 x 2010 + 2000 / 2011 x 2010 - 2020
tinh nhanh
(1-1/2010).(1-2/2010).(1-3/2010).......(1-2011/2010)
\(\left(1-\frac{1}{2010}\right).\left(1-\frac{2}{2010}\right).\left(1-\frac{3}{2010}\right)...\left(1-\frac{2011}{2010}\right)\)
\(=\left(1-\frac{1}{2010}\right).\left(1-\frac{2}{1010}\right).\left(1-\frac{3}{2010}\right)....\left(1-\frac{2010}{2010}\right).\left(1-\frac{2011}{2010}\right)\)
\(=\left(1-\frac{1}{2010}\right).\left(1-\frac{2}{2010}\right).\left(1-\frac{3}{2010}\right)...\left(1-1\right).\left(1-\frac{2011}{2010}\right)\)
\(=\left(1-\frac{1}{2010}\right).\left(1-\frac{2}{2010}\right).\left(1-\frac{3}{2010}\right)...0.\left(1-\frac{2011}{2010}\right)\)
\(=0\)
tinh nhanh
a) A=(-1).(-1)^2.(-1)^3.(-1)^4....(-1)^2010.(-1)^2011
b) B=70.(131313/565656+131313/727272+131313/909090)
d)D= -1/20+ -1/30+ -1/42+ -1/56+ -1/72+ -1/90
e) E= 5/2.1+4/1.11+3/11.2+1/2.15+13/15.4
tinh nhanh
A = 1/3 + 1/6 + 1/10 + 1/15 + 1/21 + 1/28
\(A=\frac{1}{3}+\frac{1}{6}+...+\frac{1}{28}\)
\(A=\frac{2}{6}+\frac{2}{12}+...+\frac{2}{56}\)
\(A=\frac{2}{2.3}+\frac{2}{3.4}+...+\frac{2}{7.8}\)
\(A=2\left(\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{7}-\frac{1}{8}\right)\)
\(A=2\left(\frac{1}{2}-\frac{1}{8}\right)\)
\(A=2\frac{3}{8}=\frac{3}{4}\)
Ủng hộ mk nha !!! ^_^
\(A=\frac{1}{3}+\frac{1}{6}+\frac{1}{10}+\frac{1}{15}+\frac{1}{21}+\frac{1}{28}\)
\(A=\frac{2}{6}+\frac{2}{12}+\frac{2}{20}+\frac{2}{30}+\frac{2}{42}+\frac{2}{56}\) (Tử số và mẫu số mỗi phân số nhân với 2 thì giá trị ko thay đổi)
\(A=\frac{2}{2.3}+\frac{2}{3.4}+\frac{2}{4.5}+\frac{2}{5.6}+\frac{2}{6.7}+\frac{2}{7.8}\)
\(A:2=\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}+\frac{1}{7.8}\)
\(A:2=\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}\)
\(A:2=\frac{1}{2}-\frac{1}{8}=\frac{3}{8}\)
\(A=\frac{3}{8}.2=\frac{3}{4}\)