Bài 1:

$M=3.4.5+4.5.6+...+13.14.15$

$4M=3.4.5(6-2)+4.5.6(7-3)+....+13.14.15(16-12)$

$=-2.3.4.5+3.4.5.6-3.4.5.6+4.5.6.7+....-12.13.14.15+13.14.15.16$

$=-2.3.4.5+13.14.15.16=43560$

$M=43560:4=10890$

Bài 2:

a.

$3M=\frac{3}{1.4}+\frac{3}{4.7}+\frac{3}{7.10}+...+\frac{3}{97.100}$

$=\frac{4-1}{1.4}+\frac{7-4}{4.7}+\frac{10-7}{7.10}+...+\frac{100-97}{97.100}$

$=1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+...+\frac{1}{97}-\frac{1}{100}$

$=1-\frac{1}{100}=\frac{99}{100}$

$M=\frac{99}{100}:3=\frac{33}{100}$

m: =>-5x-1-1/2x+1/3=3/2x-5/6

=>-11/2x-2/3=3/2x-5/6

=>-7x=-1/6

hay x=1/42

n: =>3x-3/2-5x-3=-x+1/5

=>-2x-9/2=-x+1/5

=>-x=47/10

hay x=-47/10

Bạn ơi xem lại hộ mk đề bài phần b với ạ, mk thấy có j đó sai sai😿😿

Bài 1

a) 3 2/5 - 1/2

= 17/5 - 1/2

= 34/10 - 5/10

= 29/10

b) 4/5 + 1/5 × 3/4

= 4/5 + 3/20

= 16/20 + 3/20

= 19/20

c) 3 1/2 × 1 1/7

= 7/2 × 8/7

= 4

d) 4 1/6 : 2 1/3

= 25/6 : 7/3

= 25/14

Bài 2

a) 3 × 1/2 + 1/4 × 1/3

= 3/2 + 1/12

= 18/12 + 1/12

= 19/12

b) 1 4/5 - 2/3 : 2 1/3

= 9/5 - 2/3 : 7/3

= 9/5 - 2/7

= 63/35 - 10/35

= 53/35

Bài 1

a) 3 2/5 - 1/2

= 17/5 - 1/2

= 34/10 - 5/10

= 29/10

b) 4/5 + 1/5 × 3/4

= 4/5 + 3/20

= 16/20 + 3/20

= 19/20

c) 3 1/2 × 1 1/7

= 7/2 × 8/7

= 4

d) 4 1/6 : 2 1/3

= 25/6 : 7/3

= 25/14

bủh

(2/3 x 4/5) x 5/6

=   8/15     x 5/6

=             4/9

(2/3 x 4/5) x 5/6 

= (5/6 x 4/5) x 2/3

=        2/3     x 2/3

=              4/9

(1/2 + 1/3) x 1/5

=   5/6        x 1/5

=               1/6

(1/2 + 1/3) x 1/5

= (1/2 x 1/5) + (1/3 x 1/5)

=       1/10    +        1/15

=                 1/6

4A6?

Đây bạn nhé

cách1\(\left(\frac{2}{3}\times\frac{4}{5}\right)\times\frac{5}{6}\)=\(\frac{8}{15}\times\frac{5}{6}\)=\(\frac{4}{9}\)cách2 =\(\left(\frac{2}{3}\times\frac{4}{5}\right)\times\frac{5}{6}\)\(\frac{2}{3}\times\frac{4}{5}\times\frac{5}{6}\)=\(\frac{40}{90}\)=\(\frac{4}{9}\)

cách1\( \left(\frac{1}{2}+\frac{1}{3}\right)\times\frac{1}{5}\)= \(\frac{5}{6}\times\frac{1}{5}\)=\(\frac{1}{6}\)cách2\( \left(\frac{1}{2}+\frac{1}{3}\right)\times\frac{1}{5}\)=\(\frac{1}{2}\times\frac{1}{5}+\frac{1}{3}\times\frac{1}{5}\)=\(\frac{1}{10}+\frac{1}{15}\)=\(\frac{25}{150}\)=\(\frac{1}{6}\)

cách1\(\left(\frac{2}{3}\times\frac{4}{5}\right)\times\frac{5}{6}\)=\(\frac{2}{3}\times\left(\frac{4}{5}\times\frac{5}{6}\right)\)=\(\frac{2}{3}\times\frac{2}{3}\)=\(\frac{4}{9}\) cách 2 \(\left(\frac{2}{3}\times\frac{4}{5}\right)\times\frac{5}{6}\)=\(\frac{2}{3}\times\frac{4}{5}\times\frac{5}{6}\)=\(\frac{2\times4\times5}{3\times5\times6}\)=\(\frac{2\times4\times5}{3\times5\times2\times3}\)=\(\frac{4}{9}\)

cách1\(\left(1\times2+\frac{1}{3}\right)\times\frac{1}{5}\)=\(\frac{7}{3}\times\frac{1}{5}\)=\(\frac{7}{15}\) cách2\(\left(1\times2+\frac{1}{3}\right)\times\frac{1}{5}\)=\(1\times\left(2+\frac{1}{3}\right)\times\frac{1}{5}\)=\(1\times\frac{7}{3}\times\frac{1}{5}\)=\(\frac{7}{3}\times\frac{1}{5}\)=\(\frac{7}{15}\)

/HT\

M = 5 + 5³ + 5⁵ + ... + 5⁴⁷ + 5⁴⁹

5²M = 5²(5 + 5³ + 5⁵ + ... + 5⁴⁷ + 5⁴⁹)

25M = 5³ + 5⁵ + 5⁷ + ... + 5⁴⁹ + 5⁵¹

25M - M = ( 5³ + 5⁵ + 5⁷ + ... + 5⁴⁹ + 5⁵¹) - (5 + 5³ + 5⁵ + ... + 5⁴⁷ + 5⁴⁹)

24M = 5⁵¹ - 5

M = \(\frac{5^{51}-5}{24}\)

Còn mấy câu kia bạn biết ko?

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