\(-\frac{10}{a}=-\frac{15}{b},b+a=5\)

\(-\frac{a}{10}=-\frac{b}{15}\)

Áp dụng tính chất dãy tỉ số bằng nhau ta có

: \(-\frac{a}{10}=-\frac{b}{15}=\frac{b+a}{-15+-10}\)

\(=-\frac{5}{25}=-\frac{1}{5}\)

\(-\frac{a}{10}=-\frac{1}{5}\Rightarrow a=-10\cdot-\frac{1}{5}=2\)

\(-\frac{b}{15}=-\frac{1}{5}\Rightarrow b=-15\cdot-\frac{1}{5}=3\)

Áp dụng tính chất dãy tỉ số bằng nhau, ta có:

\(\frac{-10}{a}\)= \(\frac{-15}{b}\)= \(\frac{-10+\left(-15\right)}{a+b}\)= \(\frac{-25}{5}\)

= -5

 Nếu mk sai thì bỏ qua nha.

giúp mình đi mình hứa sẽ k hết  luôn, ai trả lời đều đc k

a,theo t/c dãy tỉ số = nhau ta có:

a/b=b/c=c/a=a+b+c/b+c+a=1

suy ra a=b=c mà a=2021

suy ra b=2021,c=2021

suy ra b+c=2021+2021=4042

b, a²⁰²¹.b²⁰²¹/c²⁰²¹ mà a=b=c  suy ra a²⁰²¹.a²⁰²¹/a²⁰²¹=a²⁰²¹ mà a=2021 suy ra a²⁰²¹.b²⁰²¹/c²⁰²¹=2021²⁰²¹

Ta có : \(\frac{a}{b}=\frac{c}{d}=k\)

\(\Rightarrow a=bk;c=dk\)

Ta có : \(\frac{a.b}{cd}=\frac{bk.b}{dk.d}=\frac{kb^2}{kd^2}=\frac{b^2}{d^2}\)

Ta có : \(\frac{a^2-b^2}{c^2-d^2}=\frac{k^2.b^2-b^2}{k^2.d^2-d^2}=\frac{b^2\left(k-1\right)}{d^2\left(k-1\right)}=\frac{b^2}{d^2}\)

Vậy : \(\frac{ab}{cd}=\frac{a^2-b^2}{c^2-d^2}\)

vì a/b=c/d suy ra a/c=b/d

vì a/c=b/d suy ra a²/c²=b²/d²=ab/cd (1)

theo t/c dãy tỉ số = nhau ta có:

a/c=b/d=(a+b)/(c+d)

suy ra a²/c²=b²/d²=(a+b)²/(c+d)² (2)

theo t/c dãy tỉ số = nhau ta có:

a²/c²=b²/d²=a²+b²/c²+d² (3)

từ (1),(2),(3) suy ra (a+b)²/(c+d)² =a²+b²/c²+d²=ab/cd

WHAT DAY IS IT TODAY

mình cho bạn cái công thức này b/a=1/a/b

\(\frac{11}{35}=\frac{1}{\frac{35}{11}}=\frac{1}{3+\frac{2}{11}}=\frac{1}{3+\frac{1}{\frac{11}{2}}}=\frac{1}{3+\frac{1}{5+\frac{1}{2}}}\)

vậy x=3,y=5,z=2

1 – b

2 – d

3 – e

4 – a

5 – c

b,  Write T (true) or F (false) at the end of each sentence. (Điền T (đúng) hoặc F (sai) vào cuối mỗi câu.)

1. You have to work with other people when you make models.

2. People can make models of almost anything. It’s unusual for people to make architectural models.

4. You can find various models in the hobby store near your house.

5. People are advised to make simple models when they begin this hobby. Fill a word in each blank in the following passage

Gợi ý :

1. F             2. T              3. F         4. T         5. T

Bài 3. Fill a word in each blank in the following passage. (Điền từ vào chỗ trống trong đoạn văn.)

My favourite hobby is reading. I (1) _____this hobby when I was 5 years old. I still remember the first book I read, which was (2) ______a lazy rabbit. I was so excited when I read that book, so I kept (3)______I enjoy reading (4) _________ it develops my imagination. It also widens my knowledge. I can understand (5) ________ a nation has its name or what causes natural disasters. Moreover, (6) __________ helps me connect with other students because (7) ________is a book club at my school. We gather once a week to (8) _______what we have read.

Gợi ý :

(1) began

(2) about

(3) reading

(4) because

(5) why

(6) it

(7) there

(8) share

1 – b

2 – d

3 – e

4 – a

5 – c

b,  Write T (true) or F (false) at the end of each sentence. (Điền T (đúng) hoặc F (sai) vào cuối mỗi câu.)

1. F             2. T              3. F         4. T         5. T

Bài 3. Fill a word in each blank in the following passage. (Điền từ vào chỗ trống trong đoạn văn.)

My favourite hobby is reading. I (1) _____this hobby when I was 5 years old. I still remember the first book I read, which was (2) ______a lazy rabbit. I was so excited when I read that book, so I kept (3)______I enjoy reading (4) _________ it develops my imagination. It also widens my knowledge. I can understand (5) ________ a nation has its name or what causes natural disasters. Moreover, (6) __________ helps me connect with other students because (7) ________is a book club at my school. We gather once a week to (8) _______what we have read.

Gợi ý :

(1) began

(2) about

(3) reading

(4) because

(5) why

(6) it

(7) there

(8) share

2.Áp dụng................:

x/2=y/3=z/4=x+y+z/2+3+4=-18/9=-2

x/2=-2

x=-4

y/3=-2

y=-6

z/4=-2

z=-8

Vậy............

1, Áp dụng tính chất dãy tỉ số bằng nhau ta có :

\(\frac{x}{2}=\frac{y}{3}=\frac{x+y}{2+3}=\frac{15}{5}=3\)

\(\Rightarrow\hept{\frac{\frac{x}{2}=3\Rightarrow x=3.2=6}{\frac{y}{3}=3\Rightarrow y=3.3=9}}\)

Vậy x = 6 , y = 9

2 , Áp dụng tính chất dãy tỉ số bằng nhau ta có :

\(\frac{x}{2}=\frac{y}{3}=\frac{z}{4}=\frac{x+y+z}{2+3+4}=\frac{-18}{9}=-2\)

\(\Rightarrow\hept{\begin{cases}\frac{x}{2}=-2\Rightarrow x=-2.2=-4\\\frac{y}{3}=-2\Rightarrow y=-2.3=-6\\\frac{z}{4}=-2\Rightarrow z=-2.4=-8\end{cases}}\)

Vậy x = -4 , y = -6 và z = -8

ADTCDTSBN, ta có:

\(\frac{\left(x-1\right)}{2}=\frac{2\left(y-2\right)}{6}=\frac{3\left(z-3\right)}{12}\)\(=\frac{\left(x-2y+3z-6\right)}{20}=\frac{\left(14-6\right)}{8}\)=1

=>\(\hept{\begin{cases}x-1=2\\2y-4=6\\3z-9=12\end{cases}}\)\(\Leftrightarrow\hept{\begin{cases}x=3\\y=5\\z=7\end{cases}}\)

Ta có :

\(\frac{x-1}{2}=\frac{y-2}{3}=\frac{z-3}{4}\)

\(\Rightarrow\)\(\frac{x-1}{2}=\frac{2y-4}{6}\)\(=\frac{3z-9}{12}\)

Áp dụng tính chất dãy tỉ số bằng nhau, ta có :

\(\frac{x-1}{2}=\frac{2y-4}{6}\)\(=\frac{3z-9}{12}\)\(=\)\(\frac{\left(x-1\right)-\left(2y-4\right)+3z-9}{2-6+12}\)

\(=\frac{\left(x-y+z\right)+\left(-1+4-9\right)}{8}\)

\(=\frac{14-6}{8}=1\)

\(\Rightarrow\)x - 1 = 2

         y - 2 = 3

         z - 3 = 4 

\(\Rightarrow\)x = 3

         y = 5

         z = 7

\(0,1\left(2\right)=\frac{12-1}{90}=\frac{11}{90}\)

\(0,\left(27\right)=\frac{27}{99}=\frac{3}{11}\)

\(3,\left(42\right)=3+\frac{42}{99}=\frac{113}{33}\)

\(3,\left(45\right)=3+\frac{45}{99}=\frac{38}{11}\)

=38/11 nhé

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