5/8

3/4

\(a)\dfrac{3}{4}.\dfrac{5}{6}=\dfrac{5}{8}\)

\(b)\dfrac{2}{7}:\dfrac{4}{9}=\dfrac{9}{14}\)

\(\dfrac{3}{4}x\dfrac{5}{6}=\dfrac{3x5}{4x6}=\dfrac{15}{24}=\dfrac{5}{8}\)

b) \(\dfrac{2}{7}:\dfrac{4}{9}=\dfrac{2}{7}x\dfrac{9}{4}=\dfrac{18}{28}=\dfrac{9}{14}\)

1/9

\(\dfrac{1}{2}\times\dfrac{2}{3}\times\dfrac{3}{4}\times\dfrac{4}{5}\times\dfrac{5}{6}\times\dfrac{6}{7}\times\dfrac{7}{8}\times\dfrac{8}{9}\)

\(=\dfrac{1\times2\times3\times4\times5\times6\times7\times8}{2\times3\times4\times5\times6\times7\times8\times9}\)

\(=\dfrac{1}{9}\)

1/9

a; 60 \(\times\) (\(\dfrac{7}{12}\) + \(\dfrac{4}{15}\))

= 60 \(\times\) \(\dfrac{7}{12}\) + 60 \(\times\) \(\dfrac{4}{15}\)

= 35 + 16

= 51

a,\(60\times\left(\frac{7}{12}+\frac{4}{15}\right)\)\(=\frac{60\times7}{12}+\frac{60\times4}{15}\)

                                         \(=\frac{12\times5\times7}{12}+\frac{15\times4\times4}{15}\)

                                         \(=5\times7+4\times4\)

                                          \(=35+16\)                                            

                                            \(=51\)

b, \(\frac{1}{2}\times\frac{2}{3}\times\frac{3}{4}\times...\times\frac{8}{9}\)\(=\frac{1\times2\times3\times4\times5\times6\times7\times8}{2\times3\times4\times5\times6\times7\times8\times9}\)

                                                        \(=\frac{1}{9}\)

ai vhat nhìu thì kt bn với mình nha

v

\(\dfrac{11}{4}-\dfrac{9}{8}=\dfrac{22-9}{8}=\dfrac{13}{8}+\dfrac{15}{12}=\dfrac{156+120}{96}=\dfrac{276}{96}\)

\(\dfrac{126}{84}+\dfrac{5}{3}=\dfrac{378+420}{252}=\dfrac{798}{252}\)

\(\dfrac{13}{18}:\dfrac{5}{9}=\dfrac{13.5}{18.9}=\dfrac{615}{162}-\dfrac{1}{1}=\dfrac{615-162}{162}=\dfrac{453}{162}\)

\(\dfrac{3}{9}+\dfrac{45}{12}=\dfrac{36+405}{108}=\dfrac{441}{108}\)

a,11/4−9/8+15/12

=    13/8    + 15/12 

=  276/96

= 29/8

b,6/7x21/12+5/3

=  126/84 +  5/3

=   798/252

=         

c,13/18:5/9−1

=   615/162- 1

=  453/162

d,3+9/4:3/5

=  3 + 45/12

= 441/108

1+7=8, 7+8=15, 8+15= 23
Như vậy dãy số 1, 7, 8, 15, 23, đđược thành lập như sau: mỗi số trong dãy số bắt dầu từ số thứ ba là tổng của hai số đứng ngay trước nó. ( 0,5 điểm )
Dãy số được viết 1 + 7+ 8 + 15 + 23 + 38 + 61 + 99 + 160 = ( 1 điểm )
= 8 + 8 + 38 + 38 + 160 + 160 =
= 2 ( 8 + 38 + 160 ) = 
= 412

1) 1 + 7 + 8 + 15 + 23 + 38 + 61 + 99 + 160

= 1 + (8 - 1) + (15 - 7) + (23 - 8) + (38 - 15) + (61 - 23) + (99 - 38) + (160 - 61) + (259 - 99) (gạch bỏ 8 với trừ 8 ; 1 với -1 ; .....; 99 với -99)

= -7 + 160 + 259 = 412.

2) 1 + 4 + 5 + 9 + 14 + 23 + 37 + 60 + 97

= 1 + (5 - 1) + (9 - 4) + (14 - 5) + (23 - 9) + (37 - 14) + (60 - 23) + (97 - 37) + (157 - 60) (gạch bỏ 1 với -1 ; 5 với -5 ; 60 với - 60)

= -4 + 97 + 157 = 250.

tớ  chưa học xin lỗi

giúp mik zứi😭😭😭

a; 60 \(\times\) (\(\dfrac{7}{12}\) + \(\dfrac{4}{15}\)) 

 =  60 \(\times\) \(\dfrac{7}{12}\) + 60 \(\times\) \(\dfrac{4}{15}\)

= 35 + 16

= 51

b; \(\dfrac{1}{2}\) \(\times\)\(\dfrac{2}{3}\) \(\times\) \(\dfrac{3}{4}\) \(\times\) \(\dfrac{4}{5}\) \(\times\) \(\dfrac{5}{6}\) \(\times\) \(\dfrac{7}{8}\) \(\times\) \(\dfrac{8}{9}\)

= \(\dfrac{2\times3\times4\times5\times6\times7\times8}{2\times3\times4\times5\times6\times7\times8}\) \(\times\) \(\dfrac{1}{9}\)

= 1 \(\times\) \(\dfrac{1}{9}\)

= \(\dfrac{1}{9}\)

\(a,\dfrac{3}{2}\cdot x-1=\dfrac{1}{2}x-\dfrac{3}{5}\)

\(\Rightarrow\dfrac{3}{2}x-\dfrac{1}{2}x=-\dfrac{3}{5}+1\)

\(\Rightarrow\left(\dfrac{3}{2}-\dfrac{1}{2}\right)x=-\dfrac{3}{5}+\dfrac{5}{5}\)

\(\Rightarrow x=\dfrac{2}{5}\)

\(b,\dfrac{1}{2}x+\dfrac{1}{2}\left(x-2\right)=\dfrac{3}{4}-2x\)

\(\Rightarrow\dfrac{1}{2}x+\dfrac{1}{2}x+2x-1=\dfrac{3}{4}\)

\(\Rightarrow\left(\dfrac{1}{2}+\dfrac{1}{2}+2\right)x=\dfrac{3}{4}+1\)

\(\Rightarrow3x=\dfrac{7}{4}\)

\(\Rightarrow x=\dfrac{7}{4}:3\)

\(\Rightarrow x=\dfrac{7}{12}\)

\(c,\left(x-\dfrac{1}{2}\right)-\dfrac{1}{4}=0\)

\(\Rightarrow x-\dfrac{1}{2}=\dfrac{1}{4}\)

\(\Rightarrow x=\dfrac{1}{4}+\dfrac{1}{2}\)

\(\Rightarrow x=\dfrac{1}{4}+\dfrac{2}{4}\)

\(\Rightarrow x=\dfrac{3}{4}\)

\(d,4^{x-3}+1=17\)

\(\Rightarrow4^{x-3}=17-1\)

\(\Rightarrow4^{x-3}=16\)

\(\Rightarrow4^{x-3}=4^2\)

\(\Rightarrow x-3=2\)

\(\Rightarrow x=2+3\)

\(\Rightarrow x=5\)

#Toru

`3/2 x -1 =1/2x -3/5`

`=> 3/2x -1/2x = -3/5 +1`

`=> 2/2x= -3/5 + 5/5`

`=> x= 2/5`

__

`1/2x +1/2(x-2) = 3/4 -2x`

`=> 1/2x + 1/2x - 2/2 = 3/4 -2x`

`=> 1/2x +1/2x +2x = 3/4 + 1`

`=> 1/2x +1/2x + 4/2x = 3/4 +4/4`

`=> 6/2x = 7/4`

`=> x= 7/4 : 3`

`=>x=7/12`

__

`(x-1/2) -1/4=0`

`=> x-1/2=1/4`

`=> x=1/4 +1/2`

`=> x= 1/4 +2/4`

`=>x=3/4`

__

`4^(x-3) +1=17`

`=> 4^(x-3) =17-1`

`=> 4^(x-3)=16`

`=> 4^(x-3)=4^2`

`=> x-3=2`

`=>x=2+3`

`=>x=5`