Nếu khối 5 chỉ có học sinh giỏi và khá thì cuối ki không thể có chuyện cả học sinh giỏi và học sinh khá đều tăng 5 em được. 

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cậu áy nói đ

tớ tích ✔nè

B. 3

Lời giải:

Phản chứng, giả sử $a$ không cắt $b$. Suy ra $a\parallel b$

Mà: $a\perp Ox$

$\Rightarrow b\perp Ox$

Mà $b\perp Oy$

$\Rightarrow Ox\parallel Oy$ 

Điều này vô lý do $Ox$ cắt $Oy$ (bằng chứng là $\widehat{xOy}$ là góc nhọn)

Vậy điều giả sử là sai. Suy ra $a$ cắt $b$

100% ra kitsune

Lời giải:

$(2x-15)^3=(2^2.3^3-2^3.3^2):(-36)=2^2.3^2(3-2):(-36)=36:(-36)=-1$

$\Rightarrow 2x-15=-1$ hoặc $2x-15=1$

$\Rightarrow x=7$ hoặc $x=8$

Bạn lưu ý lần sau gõ đề bằng công thức toán (biểu tượng $\sum$ góc trái khung soạn thảo) để mọi người hiểu đề của bạn hơn nhé.

nhanh lên giùm e ạ

19 A

20 A

21 B

22 C

23 C

24 C

Bài nào em chưa biết cách làm thì hỏi để Thầy cô và các bạn hướng dẫn. Em không gửi một tệp bài lên nhờ mọi người giải như vậy em sẽ không học tập phát triển được.

Dạ vâng ạ!

Bài 1:

a: \(\dfrac{-3}{5}+\dfrac{7}{21}+\dfrac{-4}{5}+\dfrac{7}{5}\)

\(=\left(-\dfrac{3}{5}-\dfrac{4}{5}+\dfrac{7}{5}\right)+\dfrac{7}{21}\)

\(=\dfrac{7}{21}=\dfrac{1}{3}\)

b: \(-\dfrac{3}{17}+\left(\dfrac{2}{3}+\dfrac{3}{17}\right)\)

\(=-\dfrac{3}{17}+\dfrac{3}{17}+\dfrac{2}{3}\)

\(=0+\dfrac{2}{3}=\dfrac{2}{3}\)

c: \(\dfrac{-5}{21}+\left(\dfrac{-16}{21}+1\right)\)

\(=\left(-\dfrac{5}{21}-\dfrac{16}{21}\right)+1\)

=-1+1=0

d: \(\dfrac{5}{7}+\dfrac{9}{23}+\dfrac{-12}{7}+\dfrac{14}{23}\)

\(=\left(\dfrac{5}{7}-\dfrac{12}{7}\right)+\left(\dfrac{9}{23}+\dfrac{14}{23}\right)\)

\(=-1+1=0\)

e: \(\dfrac{3}{17}+\dfrac{-5}{13}+\dfrac{-18}{35}+\dfrac{14}{17}+\dfrac{17}{-35}+\dfrac{-8}{13}\)

\(=\left(\dfrac{3}{17}+\dfrac{14}{17}\right)+\left(-\dfrac{5}{13}-\dfrac{8}{13}\right)+\left(-\dfrac{18}{35}-\dfrac{17}{35}\right)\)

=1-1-1

=-1

f: \(\dfrac{-3}{8}\cdot\dfrac{1}{6}+\dfrac{3}{-8}\cdot\dfrac{5}{6}+\dfrac{-10}{16}\)

\(=\dfrac{-3}{8}\left(\dfrac{1}{6}+\dfrac{5}{6}\right)+\dfrac{-5}{8}\)

\(=-\dfrac{3}{8}-\dfrac{5}{8}=-1\)

g: \(\dfrac{-4}{11}\cdot\dfrac{5}{15}\cdot\dfrac{11}{-4}=\dfrac{-4}{-4}\cdot\dfrac{11}{11}\cdot\dfrac{1}{3}=\dfrac{1}{3}\)

h: \(\dfrac{7}{36}-\dfrac{8}{-9}+\dfrac{-2}{3}\)

\(=\dfrac{7}{36}+\dfrac{8}{9}-\dfrac{2}{3}\)

\(=\dfrac{7}{36}+\dfrac{32}{36}-\dfrac{24}{36}=\dfrac{15}{36}=\dfrac{5}{12}\)

i: \(\dfrac{4}{7}+\dfrac{-5}{8}-\dfrac{3}{28}\)

\(=\dfrac{32}{56}-\dfrac{35}{56}-\dfrac{6}{56}\)

\(=-\dfrac{9}{56}\)

l: \(\dfrac{-6}{11}:\left(\dfrac{3}{5}\cdot\dfrac{4}{11}\right)\)

\(=-\dfrac{6}{11}:\dfrac{12}{55}\)

\(=-\dfrac{6}{11}\cdot\dfrac{55}{12}=\dfrac{-5}{2}\)

Dài

Dạng 2:

a: \(1\dfrac{3}{4}x-5=3\dfrac{1}{3}\)

=>\(x\cdot\dfrac{7}{4}-5=\dfrac{10}{3}\)

=>\(x\cdot\dfrac{7}{4}=\dfrac{10}{3}+5=\dfrac{25}{3}\)

=>\(x=\dfrac{25}{3}:\dfrac{7}{4}=\dfrac{25}{3}\cdot\dfrac{4}{7}=\dfrac{100}{21}\)

b: \(\dfrac{2}{3}x+\dfrac{1}{4}=\dfrac{7}{12}\)

=>\(\dfrac{2}{3}x=\dfrac{7}{12}-\dfrac{1}{4}=\dfrac{7}{12}-\dfrac{3}{12}=\dfrac{4}{12}=\dfrac{1}{3}\)

=>\(x=\dfrac{1}{3}:\dfrac{2}{3}=\dfrac{1}{2}\)

c: \(\dfrac{1}{3}+\dfrac{2}{5}\left(x+1\right)=1\)

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

=>\(x+1=\dfrac{2}{3}:\dfrac{2}{5}=\dfrac{5}{3}\)

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

d: \(\dfrac{1}{4}+\dfrac{1}{3}:3x=-5\)

=>\(\dfrac{1}{3}:3x=-5-\dfrac{1}{4}=-\dfrac{21}{4}\)

=>\(3x=\dfrac{1}{3}:\dfrac{-21}{4}=\dfrac{1}{3}\cdot\dfrac{4}{-21}=\dfrac{-4}{63}\)

=>\(x=-\dfrac{4}{63}:3=-\dfrac{4}{189}\)

e: \(2x^2-72=0\)

=>\(2x^2=72\)

=>\(x^2=36\)

=>\(\left[{}\begin{matrix}x=6\\x=-6\end{matrix}\right.\)

f: \(\left(\dfrac{3}{5}x-0,75\right):\dfrac{3}{7}=2\dfrac{4}{5}\)

=>\(\left(\dfrac{3}{5}x-0,75\right):\dfrac{3}{7}=\dfrac{14}{5}\)

=>\(\dfrac{3}{5}x-0,75=\dfrac{14}{5}\cdot\dfrac{3}{7}=\dfrac{6}{5}\)

=>\(\dfrac{3}{5}x=\dfrac{6}{5}+\dfrac{3}{4}=\dfrac{39}{20}\)

=>\(x=\dfrac{39}{20}:\dfrac{3}{5}=\dfrac{39}{20}\cdot\dfrac{5}{3}=\dfrac{13}{4}\)

g: \(2x+\dfrac{3}{10}=1\dfrac{5}{6}\cdot\dfrac{6}{11}\)

=>\(2x+\dfrac{3}{10}=\dfrac{11}{6}\cdot\dfrac{6}{11}=1\)

=>\(2x=\dfrac{7}{10}\)

=>\(x=\dfrac{7}{20}\)

h: \(2\dfrac{1}{4}:\left(x-7\dfrac{1}{3}\right)=-1,5\)

=>\(\dfrac{9}{4}:\left(x-\dfrac{22}{3}\right)=-\dfrac{3}{2}\)

=>\(x-\dfrac{22}{3}=\dfrac{-9}{4}:\dfrac{3}{2}=-\dfrac{9}{4}\cdot\dfrac{2}{3}=\dfrac{-3}{2}\)

=>\(x=-\dfrac{3}{2}+\dfrac{22}{3}=\dfrac{35}{6}\)

1. Linh's car is cheaper  than Hung's car.

2. She spends 3 hours to get to the city centre.

3. I interested in collecting stamps.

4. Can you tell me the way to the National Museum, please?

5. It rains so heavily so i can't work  on time.

6. Unless the teacher arrives, the class will not start.

1 Linh's car is not as expensive as Hung's car

2 She spends 3 hours getting to the city center

3 I am interested in collecting stamps

4 Could you tell me the way to the National Museum?

5 The heavy rain prevented me from going to work on time/I can't go to work on time because of the heavy rain

6 Unless the teacher arrives, the class will not start