, x- 1/6 = 1/2+ 1/3

     x- 1/6 = 5/6

      x         = 5/6 + 1/6

       x         = 1

x - 1/6  1-1/2

x - 1/6 = 5/6

x        = 5/6 + 1/6

x        = 1 

a) A = {x = 2ⁿ| n \(\in\)N, n \(\le\)5}

b) B = {x = a²| a \(\in\)N*}

c) C = {x = 3k + 1| k \(\in\)N, k \(\le\)6}

6 phân số đó là: 3/5;3/7;3/9;5/7;5/9;7/9

5^13: 5⁷ = 5 ^13-7=5^6=15625

a⁹.a.a⁵=a⁹⁺¹⁺⁵=a¹⁵

Trả lời :

5¹³ : 5⁷ = 5^13-7 = 5⁶

a⁹ . a . a⁵ = a⁹⁺¹⁺⁵ = a¹⁵

~~Học tốt~~

a)1/1.2+1/2.3+1/3.4+....+1/1999.2000

=1-1/2+1/2-1/3+1/3-1/4+....+1/1999-1/2000

=1-1/2000

= Bn tự tính

b)=1/3.(1/1.4+1/4.7+1/7.10+...+1/100+103)

=1/3.(1-1/4+1/4-1/7+1/7-1/10+...+1/100-1/103)

=1/3.(1-1/103)

= tự làm

c)8/9-1/72-1/56-1/42-...-1/6-1/2

=8/9-(1/2+1/6+...+1/42+1/56+1/72)

=làm tương tự phần trên. Gợi ý :72=8.9 . Nói đến thế r mà ko bt làm thì chịu. yên tâm, đảm bảo đ, t học đội tuyển mà

a) \(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{1999.2000}\)

\(=\frac{2-1}{1.2}+\frac{3-2}{2.3}+\frac{4-3}{3.4}+...+\frac{2000-1999}{1999.2000}\)

\(=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{1999}-\frac{1}{2000}\)

\(=1-\frac{1}{2000}=\frac{1999}{2000}\)

b) \(\frac{1}{1.4}+\frac{1}{4.7}+\frac{1}{7.10}+...+\frac{1}{100.103}\)

\(=\frac{1}{3}\left(\frac{3}{1.4}+\frac{3}{4.7}+\frac{3}{7.10}+...+\frac{3}{100.103}\right)\)

\(=\frac{1}{3}\left(\frac{4-1}{1.4}+\frac{7-4}{4.7}+\frac{10-7}{7.10}+...+\frac{103-100}{100.103}\right)\)

\(=\frac{1}{3}\left(1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+...+\frac{1}{100}-\frac{1}{103}\right)\)

\(=\frac{1}{3}\left(1-\frac{1}{103}\right)\)

\(=\frac{34}{103}\)

c) \(\frac{8}{9}-\frac{1}{72}-\frac{1}{56}-...-\frac{1}{6}-\frac{1}{2}\)

\(=\frac{8}{9}-\left(\frac{1}{8.9}+\frac{1}{7.8}+...+\frac{1}{2.3}+\frac{1}{1.2}\right)\)

\(=\frac{8}{9}-\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{7}-\frac{1}{8}+\frac{1}{8}-\frac{1}{9}\right)\)

\(=\frac{8}{9}-\left(1-\frac{1}{9}\right)=0\)

11² = 11 x 11 = 121

Đáp số: 121

ctrl + f5

#Inosuko

11² = 121

20042004x2006/20062006×2000 = 4008000

20042004x2006/20062006×2000 = 4008000