7 Chứng minh các đẳng thức sau

a) \(a^2+b^2=\left(a+b\right)^2-2ab\) ; b) \(a^4+b^4=\left(a^2+b^2\right)^2-2a^2b^2\)

c) \(a^6+b^6=\left(a^2+b^2\right)\left[\left(a^2+b^2\right)^2-3a^2b^2\right]\)

d) \(a^6-b^6=\left(a^2-b^2\right)\left[\left(a^2+b^2\right)^2-a^2b^2\right]\)

8 Viết các biểu thức sau thành tích

a) a(b+c)+3b+3c ; b) a(c-d)+c-d ; c) b(a-c)+5a-5c

d) a(m-n)+m-n ; e) mx+my+5x+5y ; f) ma+mb-a-b

g) 4x+by+4y+bx ; h) 1-ax-x+a ; k) x^m+2-x^m

m) (a-b)^2-(b-a)(a+b) ; n) a(a-b)(a+b)-(a^2-ab+b^2)

4 Rút gọn biểu thức sau và tính giá trị của chúng:

a) 126y^3+(x-5y)(x^2+25y^2+5xy) với x=-5;y=-3

b) a^3+b^3-(a^2-2ab+b^2)(a-b) với a=-4;b=4

one day for a rabbit saw a tortoise which was crawling slowly. The rabbit laughed at the Tortoise,"how slow you are!" the toroise said," Dare you race with me? I will beat you."

The rabbit felt sure he wuold win so he accepted the challenge. The rabbit ra very fast ahead. The tortoise moved on at a slow, steady pace. Loooking round, the rabbit didn't see the tortoise. He thought that the tortoise would take long a keep up with him while he was only some hurddred metres from the finosh. He then laid down inder a tree. He fall fast asleep.

A long while later,suddenly he awoke and remembered that he was taking part in the race. He ran as possoble but it was too late. The tortoise reached the finish before him . The tortoise won the race and became the winner . The rabbit lost race and was a loser.

1 Which is the faster animal , a rabbit or a tortoise?
2 Which animal challenged to the race?
3 Was there anyone judging the competition?

4 Why did the rabbit lose the race?

1 Viết lại câu sao cho nghĩa ko đổi:
1 Ba likes visiting his grandmother on thí weekend.

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2 " Please go home a lone,Lan. "Her father said

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3 Bao is tall. He can reach the top of thí tree(enough)

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4 " You should go to school by train." My father said

5 I often went fishing on the weekend whan I live on the far6

6 "Can you bring this case into my room, Hung?" Lan said

7" Held me to plan this tree, Nam ." Hong said

8 " Can you lend me some money, Binh?" Hoa said

9 They are good teachers at maths

10 We intend to join in an English club

1 Cho tam giác ABC vuông tại A, có AB<AC. Trên cạnh BC lấy điểm D sao cho BD=BA. Kẻ AH vuông góc với BC, kẻ DK vuông góc với AC

a) Chứng minh : Góc BAD=Góc BDA

b) Chứng minh: AD là phân giác của góc HAC

c) Chứng minh : AK=AH

d) Chứng minh : AB+AC<BC+AH

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