a ) 1 1.2 + 1 2.3 + ... + 1 9.10 = 9 10 < 1.

b ) 3 2.5 + 3 5.8 + 3 8.11 + 3 11.14 + 3 14.17 + 3 17.20 = 1 2 − 1 20 < 1 2 .

c ) T a   c ó     1 2 2   < 1 1.2 ; 1 3 2 < 1 2.3 ; 1 4 2 < 1 3.4 ; ... ; 1 25 2 < 1 24.25 .

D o   đ ó , 1 2 2   + 1 3 2 + 1 4 2 + 1 25 2 < 1 1.2 + 1 2.3 + 1 3.4 + ... + 1 24.25 < 1.

a ) 1 1.2 + 1 2.3 + ... + 1 9.10 = 9 10 < 1.

b ) 3 2.5 + 3 5.8 + 3 8.11 + 3 11.14 + 3 14.17 + 3 17.20 = 1 2 − 1 20 < 1 2 .

c ) T a   c ó     1 2 2   < 1 1.2 ; 1 3 2 < 1 2.3 ; 1 4 2 < 1 3.4 ; ... ; 1 25 2 < 1 24.25 .

D o   đ ó , 1 2 2   + 1 3 2 + 1 4 2 + 1 25 2 < 1 1.2 + 1 2.3 + 1 3.4 + ... + 1 24.25 < 1.

a viết lộn hả bạn

b) 2019.(2020+1)-2019.2020

=2019.(2020+1-2020)\

=2019.1

=2019\

c)436+324.(234-1)-234.324+324

=436+324.(234-1-234+1)

=436+324.1

=436+324

=760

d)472.(36-1)+35.8

=472.35+35.8

=35.(472+8)

=35.480

=16800

Bài 1: 

a: =25+75=100

b: =60-17-43+12=12

c: =-2-18=-20

d: =-3+36-17=36-20=16

Bài 2: 

a: =-102

b: =-1000

c: =12x15=180

d: =21x(-10)=-210

B1

a 100

b 12

c -20

d 16

B2

a -102

b -1000

c 180

d -210

Bài 1:Tính

 a)(-12)+25+75+12 = 100

b)60+12+(-17)+(-43)=12
c)(-2)+(-87)+(-18)+87=-20
d)(-1)+(-2)+36+(-17)=16
Bài 2:Tính
b)8 . (-125)=-100
c)(-12) . (-15)=180
d)21 . (- 3)+(- 21 ) . 7=-210

a)

\(\left(y+1\right)^2\)

= \(y^2+2y+1\)

b)

\(\left(y-1\right)^2\)

= \(y^2-2y+1\)

a 

=y²+ 2y1 + 1²

=y² + 2y +1

b 

=y² -2y1 + 1²

=y² -2y1 + 1²

\(25\cdot69+31\cdot25-150\)
\(=25\cdot\left(69+31\right)-150\)
\(=25\cdot100-150\)
\(=2500-150\)
\(=2350\)

= 25 . ( 69 + 31 ) -150

= 25 . 100 - 150

= 2500 - 150 = 2350

=(25.69+31.25)-150

=25(69+31)-150

=25.100-150

=2500-150

=24850

a: =31,378m³

b: =8,15m³

c: =68,45m³

a: =31,378m3

b: =8,15m3

c: =68,45m3

a) 31,378m³

b) 8,15m³

c) 68,45m³

Đề bài lỗi rồi bạn, bạn xem lại nhé!

a: =20/60+12/60-15/60=17/60

b: =7/8-1/4-2/5=5/8-2/5=25/40-16/40=9/40

\(a,\dfrac{1}{3}+\dfrac{1}{5}-\dfrac{1}{4}=\dfrac{20}{60}+\dfrac{12}{60}-\dfrac{15}{60}=\dfrac{17}{60}\\ b,\dfrac{7}{8}-\left(\dfrac{1}{4}+\dfrac{2}{5}\right)=\dfrac{7}{8}-\dfrac{13}{20}=\dfrac{9}{40}\)