đoạn thứ nhất dài số mét là:

28:(3+1).3=21(m)

Bài 4:

a: a\(\perp\)c

b\(\perp\)c

Do đó: a//b

3 careless

4 bleed

V

1 Hung has colllected stamps since 2000

2 The front yard isn't large enough to play soccer in

3 Milk is delivered twice a week by the milkman

4 When did you bought this computer?

5 His car doesn't run as fasst as a race car

6 Two languages can be spoken well by Lan

VI

1 T

2 F

3 T

4 T

VII

1 Mr. Nam is arriving in Hue tonight

2 They are going back to Englang in two months

3 It is not difficult to tránlate this sentence into English

4 Would you mind lending me your dictionary?

3 careless

4 bleed

V

1 Hung has colllected stamps since 2000

2 The front yard isn't large enough to play soccer in

3 Milk is delivered twice a week by the milkman

4 When did you bought this computer?

5 His car doesn't run as fasst as a race car

6 Two languages can be spoken well by Lan

VI

1 T

2 F

3 T

4 T

VII

1 Mr. Nam is arriving in Hue tonight

2 They are going back to Englang in two months

3 It is not difficult to tránlate this sentence into English

4 Would you mind lending me your dictionary?

Bài 3: 

1: =>2x=-5/3-1/2=-10/6-3/6=-13/6

hay x=-13/12

2: =>3/5x=1/7+3/5=5/35+21/35=26/35

hay x=26/3

3: =>-3x=5/6+3/4=10/12+9/12=19/12

hay x=-19/36

4: =>1/2x=3/7-5/4=12/28-35/28=-23/28

hay x=-23/14

5: =>1/4x=-3/5-7/5=-2

hay x=-8

6: =>3x=1/42+1/7=1/42+6/42=1/7

hay x=1/21

a: Xét tứ giác ABDC có

M là trung điểm của BC

M là trung điểm của AD

Do đó: ABDC là hình bình hành

mà \(\widehat{BAC}=90^0\)

nên ABDC là hình chữ nhật

Lời giải:

Đặt \(\sqrt[3]{5\sqrt{2}+7}=m; \sqrt[3]{5\sqrt{2}-7}=n\)

\(m^3-n^3=14\)

\(mn=1\)

\((a+b+c)^3=(m-n)^3=m^3-3mn(m-n)-n^3=14-3(m-n)\)

\(\Leftrightarrow (a+b+c)^3=14-3(a+b+c)\)

\(\Leftrightarrow (a+b+c)^3+3(a+b+c)-14=0\)

\(\Leftrightarrow (a+b+c)^2[(a+b+c)-2]+2(a+b+c)(a+b+c-2)+7(a+b+c-2)=0\)

\(\Leftrightarrow (a+b+c-2)[(a+b+c)^2+2(a+b+c)+7]=0\)

Dễ thấy biểu thức trong ngoặc vuông $>0$ nên $a+b+c-2=0$

$\Leftrightarrow a+b+c=2$

$ab+bc+ac=\frac{(a+b+c)^2-(a^2+b^2+c^2)}{2}=\frac{2^2-1}{2}=\frac{3}{2}$