The Browns want to spend their coming summer vacation in Viet Nam.

(x-2)\(^2\) + (x - 3) (x + 3)

= (x)\(^2\) - 2x.2 + 2\(^2\) + x\(^2\) - 3\(^2\)

= 2x\(^2\) - 4x -5

Ta có: \(\frac{x}{1,75}\)=\(\frac{y}{0,75}\) và x-y = 4

⇒ \(\frac{x}{1,75}\)=\(\frac{y}{0,75}\)=\(\frac{x-y}{1,75-0,75}\)=\(\frac{4}{1}\)=4

⇒\(\frac{x}{1,75}\)=4 ⇔ x = 4 . 1,75 = 7

⇒\(\frac{y}{0,75}\)= 4 ⇔ y = 4 . 0,75 = 3

Vậy x = 7 ; y = 3

Ta có :

\(S\)\(\Delta\)_{^{ABC =}} \(\frac{1}{2}\)AB.AC = \(\frac{1}{2}\)AH.BC.

⇒ AB.AC = AH.BC.

⇒ AB².AC² = AH². BC².

⇔ AB².AC² = AH² (AB² + AC²).

⇒ \(\frac{1}{AH^2}\) = \(\frac{1}{AB^2}\) + \(\frac{1}{AC^2}\).

1. Match the verb phrases with the word phrases then make one situation to give a compliment

A B

1 has got beautifully at the school festival

2. has sung 10 marks in English

3. has won the first prize in the cooking contest

4 has hold a great birthday party

Ex:

Van :Lan,Minh has got 10 marks in math

Lan: Well done, Minh.

Minh: Thank you a lot

2 choose the best answers

1, He always......... me on my success

a.congratulate b. congratulations c. conglatulates

2. Let me congratulate you on pass the final contest

a.pass b.passing c.passes

3. I have an............friend.

a actively b activist c active

4. That's an.....................report

a great b excellent c good

Đặt A= 1+2+2^2+2^3+...+2^99+2^100

=>2A = 2+2²+2³+...+2¹⁰⁰+2¹⁰¹

=>2A-A = 2+2²+2³+...+2¹⁰⁰+2¹⁰¹-(1+2+2²+2³+...+2⁹⁹+2¹⁰⁰)

=> A = 2+2²+2³+...+2¹⁰⁰+2¹⁰¹-1-2-2²-2³-...-2⁹⁹-2¹⁰⁰

=2¹⁰¹-1

➤ Vậy 1+2+2^2+2^3+...+2^99+2^100 = 2¹⁰¹-1