5 12 + 1 3 2 + 3 4 − 5 6 2 = 5 12 + 4 12 2 + 9 12 − 10 12 2 = 3 4 2 + − 1 12 2 = 9 16 + 1 144 = 41 72

\(a,19^2=\left(18+1\right)^2=18^2+2.18.1+1^2=324+36+1=361\)

\(28^2=\left(27+1\right)^2=27^2+2.27.1+1^2=729+54+1=784\)

\(81^2=\left(80+1\right)^2=80^2+2.80.1+1^2=6400+160+1=6561\)

\(91^2=\left(90+1\right)^2=90^2+2.90.1+1^2=8100+180+1=8281\)

\(b,19.21=\left(20-1\right)\left(20+1\right)=20^2-1^2=400-1=399\)

\(29.31=\left(30-1\right)\left(30+1\right)=30^2-1^2=900-1=899\)

\(39.41=\left(40-1\right)\left(40+1\right)=40^2-1^2=1600-1=1599\)

\(c,28^2-8^2=\left(28-8\right)\left(28+8\right)=20.36=720\)

\(56^2-46^2=\left(56-46\right)\left(56+46\right)=10.102=1020\)

\(67^2-57^2=\left(67-57\right)\left(67+57\right)=10.124=1240\)

a) \(19^2=\left(20-1\right)^2=20^2-2.20.1+1^2=400-40+1=361\)

\(28^2=\left(30-2\right)^2=30^2-2.30.2+2^2=900-120+4=784\)

\(81^2=\left(80+1\right)^2=80^2+2.80.1+1^2=6400+160+1=6561\)

\(91^2=\left(90+1\right)^2=90^2+2.90.1+1^2=8100+180+1=8281\)

Bằng 463 bn nhoa

Cách làm là côngj 4 số đó lại roòi chia 4

(348 + 219 + 562 + 723 ) x 4 = 7412

  ( 348 + 219 + 562 + 723 ) : 4

= 1852 :4

=463

1/5 ; 2000/2000 ; 97/96 ; 562/1

Ta có : \(\frac{1}{5}< 1;\frac{97}{96}>\frac{96}{96}=1;\frac{2000}{2000}=1;\frac{562}{1}=562>1\)

Khi đó ta so sánh : \(\frac{1}{5}< \frac{2000}{2000}< \frac{97}{96}< \frac{562}{1}\)

5:

a: (2x-5)(2x+5)=4x^2-25

b: (3x-5y)(3x+5y)=9x^2-25y^2

c: (3x+7y)(3x-7y)=9x^2-49y^2

d: (2x-1)(2x+1)=4x^2-1

4:

a: 2003*2005=(2004-1)(2004+1)=2004^2-1<2004^2

b: 8(7^2+1)(7^4+1)(7^8+1)

=1/6*(7-1)(7+1)(7^2+1)(7^4+1)(7^8+1)

=1/6(7^2-1)(7^2+1)(7^4+1)(7^8+1)

=1/6(7^16-1)<7^16-1

5:

a: (2x-5)(2x+5)=4x^2-25

b: (3x-5y)(3x+5y)=9x^2-25y^2

c: (3x+7y)(3x-7y)=9x^2-49y^2

d: (2x-1)(2x+1)=4x^2-1

mik chỉ biết bài 5 thôi !

giải giùm mình đi, thanks

giải giùm mình đi nha, thanks

1) 14x - 56 = 0

 ⇔14x = 56

 ⇔x = 4

2) 4 - 2x = 0

 ⇔2x = 4

 ⇔x = 2

Đáp án B