1.Tính:
a) 35-22003
b)S=1-2+2^2-2^3+....+200^2
Tính:A= 1002 + 2002 + 3002 +...+ 10002.Biết 12+22+32+...+102=385
A=1002+2002+3002+...+10002
A=12.1002+22.1002+32.1002+...+102.1002
A=1002.(12+22+32+...+102)
A=10000.385
A=3850000
Toán
Bài 1. Tính bằng hai cách
a) (24 + 36) : 4 Cách 1 : ………………… ……………………………. ……………………………. Cách 2 : ………………… ……………………………. ……………………………. | b) (84 – 35) : 7 Cách 1 : ………………… ……………………………. ……………………………. Cách 2 : ………………… ……………………………. ……………………………. |
Bài 2. Đặt tính rồi tính:
a) 270 : 15 d. 67855 : 45
b. 32108 : 23 e. 12675 : 25
c. 26345 : 35 g. 23052 : 63
Bài 3: Cứ 25 viên gạch thì lát được 1m2 nền nhà. Hỏi nếu dùng hết 1050 viên gạch thì lát được bao nhiêu mét vuông nền nhà?
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Bài 1. Tính bằng hai cách
a) (24 + 36) : 4 Cách 1 : =60:4=15………………… ……………………………. ……………………………. Cách 2 : =24:4+36:4………………… =6 + 9 =15 …………………. ……………………………. |
Tính:
a) 1/8 x 4/5 : 6/10
b) (2/3 - 1/4) x 6/5
c) 24/35 : (4/5 x 8/7)
d) 3 + 5/7 - 1/3
a: \(\dfrac{1}{8}\cdot\dfrac{4}{5}:\dfrac{3}{5}=\dfrac{1}{10}\cdot\dfrac{5}{3}=\dfrac{1}{2\cdot3}=\dfrac{1}{6}\)
b: \(=\dfrac{8-3}{12}\cdot\dfrac{6}{5}=\dfrac{6}{12}=\dfrac{1}{2}\)
c: \(=\dfrac{24}{35}:\dfrac{32}{35}=\dfrac{3}{4}\)
d: =63/21+15/21-7/21=71/21
a \(\dfrac{1}{8}\times\dfrac{4}{5}\times\dfrac{10}{6}=\dfrac{1}{6}\)
b \(\left(\dfrac{8}{12}-\dfrac{3}{12}\right)\times\dfrac{6}{5}=\dfrac{5}{12}\times\dfrac{6}{5}=\dfrac{1}{2}\)
c \(\dfrac{24}{35}:\dfrac{32}{35}=\dfrac{24}{35}\times\dfrac{35}{32}=\dfrac{3}{4}\)
d \(\dfrac{63}{21}+\dfrac{15}{21}-\dfrac{7}{21}=\dfrac{71}{21}\)
Tính:A: 1+1/3+1/6+1/10+...+1/171+1/190.
B: S=1/2+1/2^2+1/2^3+...+1/2^20.
C: 1+2+2^2+2^3+...+2^2006+2^2007.
A= 1 +\(\frac{1}{3}\)+\(\frac{1}{6}\)+ .....+ \(\frac{1}{171}\)+\(\frac{1}{190}\)
A= 1 +2.(\(\frac{1}{6}\)+\(\frac{1}{12}\)+....+\(\frac{1}{342}\)+\(\frac{1}{380}\))
A=1+ 2.(\(\frac{1}{2.3}\)+\(\frac{1}{3.4}\)+....+\(\frac{1}{18.19}\)+\(\frac{1}{19.20}\))
A=1+2.(\(\frac{1}{2}\)-\(\frac{1}{3}\)+\(\frac{1}{3}\)-\(\frac{1}{4}\)+......+\(\frac{1}{18}\)-\(\frac{1}{19}\)+\(\frac{1}{19}\)-\(\frac{1}{20}\))
A=1 +2.(\(\frac{1}{2}\)-\(\frac{1}{20}\))
A=1+2.\(\frac{9}{20}\)=1+\(\frac{9}{10}\)=\(\frac{19}{10}\)
B=\(\frac{1}{2}\)+\(\frac{1}{2^2}\)+\(\frac{1}{2^3}\)+....+\(\frac{1}{2^{20}}\)
2B= 1 +\(\frac{1}{2}\)+\(\frac{1}{2^2}\)+\(\frac{1}{2^3}\)+......+\(\frac{1}{2^{21}}\)
2B-B= 1-\(\frac{1}{2^{21}}\)
B=1-\(\frac{1}{2^{21}}\)
C= 1 +2+ \(2^2\)+\(2^3\)+.......+\(2^{2007}\)
2C=2 + \(2^2\)+\(2^3\)+.....+\(2^{2007}\)+ \(2^{2008}\)
2C-C= \(2^{2008}\)-1
C=\(2^{2008}\)-1
Tính:A: 1+1/3+1/6+1/10+...+1/171+1/190.
B: S=1/2+1/2^2+1/2^3+...+1/2^20.
C: 1+2+2^2+2^3+...+2^2006+2^2007.
\(A=1+\frac{2}{6}+\frac{2}{12}+...+\frac{2}{380}\)
\(=1+\frac{2}{2.3}+\frac{2}{3.4}+...+\frac{2}{19.20}\)
\(=1+2\left(\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{19}-\frac{1}{20}\right)\)
\(=1+2\left(\frac{1}{2}-\frac{1}{20}\right)\)
\(=1+2\times\frac{9}{20}\)
\(=1+\frac{9}{10}\)
\(=\frac{19}{10}\)
b)\(2S=2\left(\frac{1}{2}+\frac{1}{2^2}+...+\frac{1}{2^{20}}\right)\)
\(2S=1+\frac{1}{2}+...+\frac{1}{2^{19}}\)
\(2S-S=\left(1+\frac{1}{2}+...+\frac{1}{2^{19}}\right)-\left(\frac{1}{2}+\frac{1}{2^2}+...+\frac{1}{2^{20}}\right)\)
\(S=1-\frac{1}{2^{20}}\)
c)đặt A=1+2+2^2+2^3+...+2^2006+2^2007.
2A=2(1+2+2^2+2^3+...+2^2006+2^2007)
2A=2+2^2+2^3+...+2^2008
2A-A=(2+2^2+2^3+...+2^2008)-(1+2+2^2+2^3+...+2^2006+2^2007)
A=2^2008-1
Tính:
A.3 giờ 42 phút+1 giờ 37 phút=.............
B.14 giờ 18 phút-6 giờ 42 phút=......
C.2 giờ 35 phút*3=.........
D.35 giờ 40 phút:5=............
5 giờ 19 phút
7 giờ 36 phút
7 giờ 35 phút
7 giờ 8 phút
1/Tính:
a. S=\(\dfrac{5^2}{1.6}\) + \(\dfrac{5^2}{6.11}\)+ \(\dfrac{5^2}{11.16}\) + \(\dfrac{5^2}{16.21}\) + \(\dfrac{5^2}{21.26}\)
b. (1 - \(\dfrac{1}{2}\)) . (1 - \(\dfrac{1}{3}\) ) . (1- \(\dfrac{1}{4}\) ) . ( 1 - \(\dfrac{1}{5}\) ) .... ( 1 - \(\dfrac{1}{19}\) ) . ( 1 - \(\dfrac{1}{20}\))
Mk cần gấp lắm ~help me please~
Giải:
a) S=52/1.6+52/6.11+52/11.16+52/16.21+52/21.26
S=5.(5.1/6+5/6.11+5/11.16+5/16.21+5/21.26)
S=5.(1/1-1/6+1/6-1/11+1/11-1/16+1/16-1/21+1/21-1/26)
S=5.(1/1-1/26)
S=5.25/26
S=125/26
b) (1-1/2).(1-1/3).(1-1/4).(1-1/5).....(1-1/19).(1-1/20)
=1/2.2/3.3/4.4/5.....18/19.19/20
=1.2.3.4.....18.19/2.3.4.5.....19.20
=1/20
Chúc bạn học tốt!
Tính:
a)S = a + a^3 + a^5 +...+ a^2n+1,với (a>=2, n thuộc N*)
b)S1 = 1 + a^2 + a^4 + a^6 +...+ a^2n,với (a>=2, n thuộc N)
\(S=a+a^3+...+a^{2n+1}\)
\(S.a^2=a^3+a^5+...+a^{2n+1}+a^{2n+3}\)
\(\Rightarrow S\left(a^2-1\right)=a^{2n+3}-a\)
\(\Rightarrow S=\dfrac{a^{2n+3}-a}{a^2-1}\)
\(S_1=1+a^2+...+a^{2n}\)
\(S_1.a^2=a^2+a^4+...+a^{2n}+a^{2n+2}\)
\(\Rightarrow S_1\left(a^2-1\right)=a^{2n+2}-1\)
\(\Rightarrow S_1=\dfrac{a^{2n+2}-1}{a^2-1}\)
a/ Tính tổng: S = (-1/3)^0 + (-1/3)^1 + (-1/3)^2 + ... +(-1/3)^200
b/ CMR: S = 1/2! + 2/3! + 3/4! +...+ 199/200! < 1