5/8 x 6 + 1/3 = 15/4 + 1/3 = 49/12

5/4- 1/3 = 15/12 - 4/12 = 11/12

a) = 15/4 + 1/3 = 49/12

b) = 5/4 - 1/3 = 11/12

ta có:  f(x) + g(x) = ( 7 x^6 - 6x ^5 +5x^4 -4x^3 +3x^2 -2x +1) - ( x - 2x^2 +3x^3 - 4x^4 + 5x^5 - 6x^6)

                          \(=7x^6-6x^5+5x^4-4x^3+3x^2-2x+1-x+2x^2-3x^3+4x^4-5x^5+6x^6\)

                      \(=\left(7x^6+6x^6\right)-\left(6x^5+5x^5\right)+\left(5x^4+4x^4\right)-\left(4x^3+3x^3\right)+\left(3x^2+2x^2\right)-\left(2x+x\right)+1\)

\(=13x^6-11x^5+9x^4-7x^3+5x^2-3x+1\)

Chúc bn học tốt !!!!!!

Uhhhhhhhhhhhhhhhhhhhhhhhhhh😥😥😥😥😥😥😥😥😥😥😥????????????...............

Bài 1: 

Ta có:

\(y-x=25\Rightarrow y=25+x\)

Mà \(7x=4y\Rightarrow7x=4\cdot\left(25+x\right)\)

\(7x=100+4x\)

\(\Rightarrow7x-4x=100\)

\(3x=100\)

\(x=\frac{100}{3}\)

bài 1 :

Ta có: 7x=4y ⇔ x/4=y/7

áp dụng tính chất dãy tỉ số bằng nhau ta có 

x/4=y/7=(y-x)/(7-4)=100/3

⇒x= 4 x 100/3=400/3 ; y = 7 x 100/3=700/3

bài 2 

ta có x/5 = y/6 ⇔ x/20=y/24

         y/8 = z/7 ⇔ y/24=z/21

⇒x/20=y/24=z/21

ADTCDTSBN(bài 1 có)

x/20=y/24=z/21=(x+y)/(20+24)=69/48=23/16

⇒x= 20 x 23/16 = 115/4

   y= 24x 23/16=138/2

   z=21x23/16=483/16

bài 3

x:y:z=3:8:5  ⇔ x/3=y/8=z/5

ADTCDTSBN

x/3=y/8=z/5=(3x+y-4z)/(9+8-10)=14/7=2

⇒x = 2x3 = 6 ; y= 2x8=`16; z=2x5=10

1+1=2

2+2=4

3+3=6

4+4=8

5+5=10

1+2+3+4+5+6+7+8+9+10=55

2

4

6

8

10

55

1+1=2 

2+2= 4 

3+3= 6  

4+4= 8 

5+5= 10 

1+2+3+4+5+6+7+8+9+10= 55 

kb nhé hok tốt

Câu b

Ta có :x + 3 /1.3  +3/3.5 + 3/5.7+...+3/13.15=2 1/5

X + 2/3.(1-1/3+1/3-1/5+1/5-1/7+...+1/13-1/15)1=11/5

X+2/3.(1-1/15)=11/5

X+ 2/3.14/15=11/5

X + 28/45=11/5

X = 11/5 -28/45

X=71/45

Câu a  gợi ý 

1/2-1/3/1/6=0 

1/2- 1/3 - 1/6 ) x (1/2 + 2/3 + 3/4 +4/5 + .......+ 2019 /2020 ) =0 

3/4:x=9/10

X = 3/4:9/10

X = 5/6

Câu b

Ta có : x + 3 /1.3  +3/3.5 + 3/5.7+...+3/13.15 = 2 1/5

X + 2/3.(1-1/3+1/3-1/5+1/5-1/7+...+1/13-1/15)1 = 11/5

X + 2/3.(1-1/15) = 11/5

X + 2/3.14/15 = 11/5

X + 28/45 = 11/5

X = 11/5 - 28/45

X = 71/45

đúng 100% nhé

a) \(\frac{1}{2}\times\frac{1}{3}+\frac{1}{3}\times\frac{1}{4}+\frac{1}{4}\times\frac{1}{5}+\frac{1}{5}\times\frac{1}{6}=\frac{1}{2\times3}+\frac{1}{3\times4}+\frac{1}{4\times5}+\frac{1}{5\times6}\)

                                                                                      \(=\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}\)

                                                                                     \(=\frac{1}{2}-\frac{1}{6}=\frac{3}{6}-\frac{1}{6}=\frac{2}{6}=\frac{1}{3}\)

b) \(\left(1-\frac{1}{2}\right)\left(1-\frac{1}{3}\right)\left(1-\frac{1}{4}\right)=\frac{1}{2}\times\frac{2}{3}\times\frac{3}{4}=\frac{1}{4}\)

\(a)\frac{1}{2}\times\frac{1}{3}+\frac{1}{3}\times\frac{1}{4}+\frac{1}{4}\times\frac{1}{5}+\frac{1}{5}\times\frac{1}{6}\)

\(\Rightarrow\frac{1}{2\times3}+\frac{1}{3\times4}+\frac{1}{4\times5}+\frac{1}{5\times6}\)

\(\Rightarrow\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}\)

\(\Rightarrow\frac{1}{2}-\frac{1}{6}\)

\(\Rightarrow\frac{1}{3}\)

\(b)\left(1-\frac{1}{2}\right)\times\left(1-\frac{1}{3}\right)\times\left(1-\frac{1}{4}\right)\)

\(=\frac{1}{2}\times\frac{2}{3}\times\frac{3}{4}\)

\(=\frac{1\times2\times3}{2\times3\times4}\)

\(=\frac{1}{4}\)

\(b)\left(1-\frac{1}{2}\right)\div\left(1-\frac{1}{3}\right)\div\left(1-\frac{1}{4}\right)\)

\(=\frac{1}{2}\div\frac{2}{3}\div\frac{3}{4}\)

\(=\frac{1}{2}\times\frac{3}{2}\times\frac{4}{3}\)

\(=\frac{1\times3\times2\times2}{2\times2\times3}\)

\(=1\)

Câu 1: 

a) \(\frac{3}{2}.\frac{4}{5}-x=\frac{2}{3}\)

\(\frac{6}{5}-x=\frac{2}{3}\)

\(x=\frac{8}{15}\)

b) \(\frac{6}{7}:\frac{1}{2}.\frac{3}{4}-\frac{5}{8}=\frac{37}{56}\)

Câu 2:

Gọi số có hai chữ số cần tìm là: ab

ta có: ab2  = ab + 92

=> a x 100 + b x 10 + 2 = a x 10 + b + 92

=> a x 90 + b x 9 = 90

9 x ( a x 10 + b) = 90

a x 10 + b = 90 : 9

a x 10 + b = 10 = 1 x 10 + 0

=> a = 1; b = 0

KL: ab = 10

Câu 1 :

a) \(\frac{3}{2}\times\frac{4}{5}-x=\frac{2}{3}\)

\(\Rightarrow\frac{6}{5}-x=\frac{2}{3}\)

\(\Rightarrow x=\frac{6}{5}-\frac{2}{3}\)

\(\Rightarrow x=\frac{8}{15}\)

b) Ko rõ đề :)

Câu 2 :

Gọi số cần tìm là \(\overline{ab}\), ta có :

\(\overline{ab2}-\overline{ab}=92\)

\(\Rightarrow\overline{ab}\times10+2-\overline{ab}=92\)

\(\Rightarrow\overline{ab}\times9+2=92\)

\(\Rightarrow\overline{ab}\times9=90\)

\(\Rightarrow\overline{ab}=90:9\)

\(\Rightarrow\overline{ab}=10\)

Học tốt # ^-<