đề bài em

35 - (27 + \(x\)) chứ em?

Khoảng cách : `5`

Số số hạng là :

\(\dfrac{526-11}{5}+1=104\)

Tổng dãy là :

\(\dfrac{\left(526+11\right)\times104}{2}=27924\)

h=11+16+...+526=\(\dfrac{\left(526-11\right):5+1\cdot\left(11+526\right)}{2}\)=\(\dfrac{104\cdot537}{2}\)=27924.

(72x135+9x28x15):25-3500:25

=(72x135+28x135-3500):25

=((72+28)x135-3500):25

=(13500-3500):25

=10000:25=400

(72x135+9x28x15):25-3500:25

=(72x135+72x28):25-3500:25

=135x(72+28):25-3500:25  

=135x100:25-3500:25

=13500:25-3500:25

=(13500-3500):25

=10000:25

=400

103

=37+-63+201-135+63

=37+201-135+(-36+63)

=238-135+0

=103

chịu

Câu 20:

Ta có: \(A=40.22\cdot75-30.22\cdot55+40.22\cdot25-30.22\cdot45\)

\(=40.22\left(75+25\right)-30.22\left(55+45\right)\)

\(=100\cdot\left(40.22-30.22\right)\)

\(=100\cdot10=1000\)

\(x^2\left(x-5\right)+5-x=0\\ \Rightarrow\left(x-5\right)\left(x^2-1\right)=0\\ \Rightarrow\left[{}\begin{matrix}x=5\\x=-1\\x=1\end{matrix}\right.\)

\(\Leftrightarrow x^2\left(x-5\right)-\left(x-5\right)=0\)

\(\Leftrightarrow\left(x^2-1\right)\left(x-5\right)=0\)

\(\Leftrightarrow\left(x-1\right)\left(x+1\right)\left(x-5\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x-1=0\\x+1=0\\x-5=0\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x=1\\x=-1\\x=5\end{matrix}\right.\)

Bài 21

1 are

2 enjoy reading

3 loves reading 

4 learns

5 ;oles

6 spends

7 thinks 

8talks

9 lasts

10 agree

11 will go

12 will be

13 will buy

14 will be

15 will probably join

16 have

17 will go

18 enjoy

a) Yes, they do

b) Because there are many interesting things

c) They talk about the books

d) Tomorrow

e) they will go home and enjoy their books