A = (2 + 2²) + (2³ + 2⁴ ) +…(2¹⁹⁹ + 2²⁰⁰)

A = 6 + 2² (2 + 2² ) +… + 2¹⁹⁸ (2 + 2²)

A = 6 + 2² (6 ) +… + 2¹⁹⁸ (6)

A = 6(1 + 2² +… + 2¹⁹⁸)

Vậy A chia hết cho 6

a) \(\left(\frac{2}{7}+\frac{3}{8}+\frac{12}{7}+\frac{5}{8}\right).\frac{19}{36}\)

\(=\left\{\left(\frac{2}{7}+\frac{12}{7}\right)+\left(\frac{3}{8}+\frac{5}{8}\right)\right\}.\frac{19}{36}\)

\(=\left(\frac{14}{7}+\frac{8}{8}\right).\frac{19}{36}\)

\(=\left(2+1\right).\frac{19}{36}\)

\(3.\frac{19}{36}=\frac{19}{12}\)

Ta có :

\(A=\frac{1}{3}-\frac{3}{4}-\left(-\frac{3}{5}\right)+\frac{1}{72}-\frac{2}{9}-\frac{1}{36}+\frac{1}{15}\)

\(\Rightarrow A=\frac{5}{15}-\frac{54}{72}+\frac{9}{15}+\frac{1}{72}-\frac{16}{72}-\frac{1}{72}+\frac{1}{15}\)

\(\Rightarrow A=\left(\frac{5}{15}+\frac{9}{15}+\frac{1}{15}\right)+\left(-\frac{54}{72}+\frac{1}{72}-\frac{16}{72}-\frac{2}{72}\right)\)

\(\Rightarrow A=1-\frac{71}{72}=\frac{1}{72}\)

1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10 + 11 + 12 

= ( 1 + 12 ) + ( 2 + 11 ) + ( 3 + 10 ) + ( 4 + 9 ) + ( 5 + 8 ) + ( 6 + 7 ) 

=     13         +     13       +     13       +      13     +    13      + 13

=               13 x 6 

=                 78

sai thui

1+2+3+4+5+6+7+8+9+10+11+12

=(1+9)+(2+8)+(3+7)+(4+6)+(5+10)+(11+12)

=10+10+10+10+15+23

=10×4+15+23

=40+15+23

=55+23

=78

ủng hộ nha có gì sai sót mong bạn thông cảm cho !!!

1 + 2 + 3 + 4 +5 + 6 + 7 + 8 + 9 + 10 +11 + 12

= ( 12 + 8 ) + ( 11 + 9 ) + ( 7 + 3 ) + ( 6 + 4 ) + ( 10 + 2 + 3 ) + 1

Mình cũng không biết nữa !

 36-4x9 = 36 - 36 = 0 Vì số nào nhân với 0 thì cũng bằng 0 nên phép tính đó bằng 0

TL

1+2+3+4+5+6+7+8+9=45

nha bn

HT

1+2+3+...+9

=(1+9)+(2+8)+...+5

=10+10+...+5

=10.4+5

=45

HT

45

nha bn

HT

OK

giúp nhanh ạ, mình cần gấp

Bài 5:

a: =1/3+2/5

=5/15+6/15

=11/15

b: =6/21+12/21=18/21=6/7

c: =16/24+10/24

=26/24

=13/12

d: =4/12+3/12+10/12

=17/12

e: =19/24-9/24

=10/24

=5/12

f: =8/9-3/9=5/9

g: =9/3+1/3=10/3

k: =15/24+42/24+14/24

=71/24

+1

\(a,\\ =\left(\dfrac{4}{9}+\dfrac{5}{9}\right)+\left(\dfrac{1}{8}+\dfrac{7}{8}\right)=1+1=2\\ b,\\ =\left(\dfrac{1}{3}+\dfrac{4}{3}+\dfrac{2}{3}\right)\left(\dfrac{5}{12}+\dfrac{1}{12}\right)\\ =\dfrac{7\times2}{3\times2}+\dfrac{1\times3}{2\times3}=\dfrac{14+3}{6}=\dfrac{17}{6}\)

\(a,\dfrac{4}{9}+\dfrac{1}{8}+\dfrac{5}{9}+\dfrac{7}{8}=\left(\dfrac{4}{9}+\dfrac{5}{9}\right)+\left(\dfrac{1}{8}+\dfrac{7}{8}\right)=\dfrac{9}{9}+\dfrac{8}{8}=1+1=2\\ b,\dfrac{1}{3}+\dfrac{2}{3}+\dfrac{5}{12}+\dfrac{4}{3}+\dfrac{1}{12}=\left(\dfrac{1}{3}+\dfrac{2}{3}+\dfrac{4}{3}\right)+\left(\dfrac{5}{12}+\dfrac{1}{12}\right)=\dfrac{7}{3}+\dfrac{6}{12}=\dfrac{7}{3}+\dfrac{1}{2}=\dfrac{14}{6}+\dfrac{3}{6}=\dfrac{17}{6}\)

a: \(=\left(\dfrac{4}{9}+\dfrac{5}{9}\right)+\left(\dfrac{1}{8}+\dfrac{7}{8}\right)\\ =1+1=2\)

b: \(=\left(\dfrac{1}{3}+\dfrac{2}{3}\right)+\left(\dfrac{5}{12}+\dfrac{1}{12}\right)+\dfrac{4}{3}\\ =1+\dfrac{1}{2}+\dfrac{4}{3}=\dfrac{17}{6}\)

1.a,=(54+45+1).113

=100.113

=11300

b,=(3/7+8/14)+(4/9+10/18)

=1+1

=2

2.a,=13/10+1/3

=49/30

b,=12/9.(1/12+1/6)

=12/9.1/4

=1/3

c,=3/4.3/2

=9/8

d,=3/2-1/3

=7/6

1:tính bằng cách thuận tiện nhất:

a)54 x 113 + 45 x 113 + 113

= 54 x 113 + 45 x 113 + 113x1

=113 x(54+45+1)

= 113x100

=1300

 b)3/7 + 4/9 + 8/14 + 10/18

=(3/7+8/14)+(4/9+10/18)

=    1           + 1

=2