Bài 1: Tính nhanh:

A = 3/1*2 + 3/2*3 + 3/3*4 + ... + 3/399*400

=>3A = 1/1*2 + 1/2*3 + 1/3*4 + ... + 1/399*400

    3A = 1 - 1/2 + 1/2 - 1/3 + 1/3 - 1/4 + ... + 1/399 - 1/400

    3A = 1 - 1/400

      3A = 400/400 - 1/400

      3A = 399/400

        A = 399/400 : 3

        A = 399/400 . 1/3

        A = 133/400.

Có gì ko hiểu bn ib mk nha.^^

\(A=\frac{3}{1.2}+\frac{3}{2.3}+\frac{3}{3.4}+...+\frac{3}{399.400}\)

\(A=3.\left(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{399.400}\right)\)

\(A=3.\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{399}-\frac{1}{400}\right)\)

\(A=3.\left(1-\frac{1}{400}\right)\)

\(A=3.\frac{399}{400}\)

\(A=\frac{1197}{400}\)

\(B=\frac{5}{1.2}+\frac{5}{2.3}+\frac{5}{3.4}+...+\frac{5}{399.400}\)

\(B=5.\left(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{399.400}\right)\)

\(B=5.\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{399}-\frac{1}{400}\right)\)

\(B=5.\left(1-\frac{1}{400}\right)\)

\(B=5.\frac{399}{400}\)

\(B=\frac{399}{80}\)

\(C=\frac{2}{5.7}+\frac{2}{7.9}+\frac{2}{9.11}+...+\frac{2}{149.151}\)

\(C=\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+\frac{1}{9}-\frac{1}{11}+...+\frac{1}{149}-\frac{1}{151}\)

\(C=\frac{1}{5}-\frac{1}{151}\)

\(C=\frac{146}{755}\)

\(D=\frac{3}{5.7}+\frac{3}{7.9}+\frac{3}{9.11}+...+\frac{3}{149.151}\)

\(D=\frac{3}{2}.\left(\frac{2}{5.7}+\frac{2}{7.9}+\frac{2}{9.11}+...+\frac{2}{149.151}\right)\)

\(D=\frac{3}{2}.\left(\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+\frac{1}{9}-\frac{1}{11}+...+\frac{1}{149}-\frac{1}{151}\right)\)

\(D=\frac{3}{2}.\left(\frac{1}{5}-\frac{1}{151}\right)\)

\(D=\frac{3}{2}.\frac{146}{755}\)

\(D=\frac{219}{755}\)

\(E=\frac{11}{1.3}+\frac{11}{3.5}+\frac{11}{5.7}+...+\frac{11}{99.101}\)

\(E=\frac{11}{2}.\left(\frac{2}{1.3}+\frac{2}{3.5}+\frac{2}{5.7}+...+\frac{2}{99.101}\right)\)

\(E=\frac{11}{2}.\left(1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{99}-\frac{1}{101}\right)\)

\(E=\frac{11}{2}.\left(1-\frac{1}{101}\right)\)

\(E=\frac{11}{2}.\frac{100}{101}\)

\(E=\frac{550}{101}\)

_Chúc bạn học tốt_

a: \(=\dfrac{10-6}{15}\cdot\dfrac{1}{3}=\dfrac{4}{45}\)

b: \(=\dfrac{10+6}{15}\cdot\dfrac{1}{3}=\dfrac{16}{45}\)

c: \(=\dfrac{4+3}{6}\cdot\dfrac{4}{3}=\dfrac{7\cdot4}{6\cdot3}=\dfrac{28}{18}=\dfrac{14}{9}\)

d: \(=\dfrac{20-14}{35}\cdot\dfrac{9}{4}=\dfrac{6}{35}\cdot\dfrac{9}{4}=\dfrac{54}{140}=\dfrac{27}{70}\)

a (2/3 - 2/5 ) nhân 1/3

C1) 

=4/15 x 1/3

= 4/45

C2)

2/3 x 1/3 - 2/5 x 1/3

= 2/9 - 2/15

= 4/45

b (2/3 + 2/5 )nhân 1/3

GIỐNG CÂU A

c (2/3 + 1/2 ) chia 3/4

C1) =7/6 : 3/4

= 14/9

C2) 

2/3 : 3/4 + 1/2 : 3/4

= 8/9 + 2/3

= 14/9

d(4/7 - 2/5 ) chia 4/9

C1) 

= 6/35 : 4/9

= 27/70

C2)

4/7 : 4/9 - 2/5 : 4/9

= 9/7 -9/10

= 27/70

a) C1 : \(\left(\dfrac{2}{3}-\dfrac{2}{5}\right)\times\dfrac{1}{3}=\dfrac{4}{15}\times\dfrac{1}{3}=\dfrac{4}{45}\)

    C2 : \(\left(\dfrac{2}{3}-\dfrac{2}{5}\right)\times\dfrac{1}{3}=\dfrac{2}{3}\times\dfrac{1}{3}-\dfrac{2}{5}\times\dfrac{1}{3}=\dfrac{2}{9}-\dfrac{2}{15}=\dfrac{4}{45}\)

b) C1 \(\left(\dfrac{2}{3}+\dfrac{2}{5}\right)\times\dfrac{1}{3}=\dfrac{16}{15}\times\dfrac{1}{3}=\dfrac{16}{45}\)

    C2 \(\left(\dfrac{2}{3}+\dfrac{2}{5}\right)\times\dfrac{1}{3}=\dfrac{2}{3}\times\dfrac{1}{3}+\dfrac{2}{5}\times\dfrac{1}{3}=\dfrac{2}{9}+\dfrac{2}{15}=\dfrac{16}{45}\)

c) C1 \(\left(\dfrac{2}{3}+\dfrac{1}{2}\right):\dfrac{3}{4}=\left(\dfrac{2}{3}+\dfrac{1}{2}\right)\times\dfrac{4}{3}=\dfrac{7}{6}\times\dfrac{4}{3}=\dfrac{14}{9}\)

   C2 \(\left(\dfrac{2}{3}+\dfrac{1}{2}\right):\dfrac{3}{4}=\left(\dfrac{2}{3}+\dfrac{1}{2}\right)\times\dfrac{4}{3}=\dfrac{2}{3}\times\dfrac{4}{3}+\dfrac{1}{2}\times\dfrac{4}{3}=\dfrac{8}{9}+\dfrac{2}{3}=\dfrac{14}{9}\)

d) C1 \(\left(\dfrac{4}{7}-\dfrac{2}{5}\right):\dfrac{4}{9}=\left(\dfrac{4}{7}-\dfrac{2}{5}\right)\times\dfrac{9}{4}=\dfrac{6}{35}\times\dfrac{9}{4}=\dfrac{27}{70}\)

    C2 \(\left(\dfrac{4}{7}-\dfrac{2}{5}\right):\dfrac{4}{9}=\left(\dfrac{4}{7}-\dfrac{2}{5}\right)\times\dfrac{9}{4}=\dfrac{4}{7}\times\dfrac{9}{4}-\dfrac{2}{5}\times\dfrac{9}{4}=\dfrac{36}{28}-\dfrac{9}{10}=\dfrac{27}{70}\)

1) 1/3 x 1/2 x 3/7 = 3/42 = 1/14

2) 5/4 x 1/3 +1/7 = 5/12 + 1/7 = 35/84 + 12/84 = 47/84

3) 8 x ( 8/9 - 2/3 ) = 8 x 2/9 = 16/9

4) 5/6 x 48/20 x 1/2 = 240/240 = 1

5) ( 2/5 + 3/4 ) + 8 = 23/20 + 8 = 23//20 + 160/20 = 183/20

6) 10 x ( 1/2 - 1/5 ) = 10 x 3/10 = 10/1 x 3/10 = 30/10 = 3

e tách ra nhé.☘

;))

1: \(=\dfrac{1}{3}\cdot\dfrac{3}{7}\cdot\dfrac{1}{2}=\dfrac{1}{7\cdot2}=\dfrac{1}{14}\)

2: =5/12+1/7

=35/84+12/84=47/84

3: =8(8/9-6/9)

=8*2/9=16/9

4: \(=\dfrac{5}{12}\cdot\dfrac{12}{5}=1\)

5: =16/5+6

=16/5+30/5=46/5

6: =10*1/2-10*1/5

=5-2=3

Em nên gõ công thức trực quan để đề bài rõ ràng nhé

4:

a: =4/15-2,9+11/15=1-2,9=-1,9

b: \(=-36,75+3,7-63,25+6,3=10-100=-90\)

c: \(=6,5+3,5-\dfrac{10}{17}-\dfrac{7}{17}=10-1=9\)

d: \(=\dfrac{13}{25}\left(-39,1-60,9\right)=\dfrac{13}{25}\left(-100\right)=-52\)

e: =-5/12-7/12-3,7-6,3=-1-10=-11

f: =2,8(-6/13-7/13)-7,2=-2,8-7,2=-10

cậu tách ra từng bài thôi nha.

sai

sai

đúng

sai

\(37\left(3+7\right)=3^3+7^3\)

\(37\cdot10=27+343\)

\(370=370\)(thảo mãn

=>đúng

vậy 37(3+7)=3^3+7^3

59 nhân 9 ( 5 + 9 ) = 5 mũ 3  + 9 mũ 3

( 1 + 2 + 3 + 4 ) mũ 2 = 1 mũ 2 +2 mũ 2 + 3 mũ 2 + 4 mũ 2

( 1 + 2 +3 +4 ) mũ 2 = 1 mũ 3 + 2 mũ 3 + 3 mũ 3 + 4 mũ 3

\(59\cdot9\left(5+9\right)=5^3+9^3\)

\(531\cdot14=125\cdot729\)

\(7434=91125\)(ko thỏa mãn)

vậy \(59\cdot9\left(5+9\right)=5^3+9^3\)là sai

Nhìn nó rối ghê á

1: =-15+10-35+28=-32

rối thật đó