cái này áp dụng hệ thức lượng thôi bạn

AH=căn 6^2-4,8^2=3,6cm

=>AC=6^2/3,6=10cm

dạ em cám onnnn

Chọn D

tai sao vay a?

a: \(\frac{a\sqrt{b}+b\sqrt{a}}{\sqrt{a}+\sqrt{b}}\)

\(=\frac{\sqrt{ab}\left(\sqrt{a}+\sqrt{b}\right)}{\sqrt{a}+\sqrt{b}}=\sqrt{ab}\)

Ta có: \(\frac{\sqrt{a^3}-\sqrt{a^2b}+\sqrt{ab^2}-\sqrt{b^3}}{\sqrt{a}-\sqrt{b}}\)

\(=\frac{a\cdot\sqrt{a}-a\cdot\sqrt{b}+b\cdot\sqrt{a}-b\cdot\sqrt{b}}{\sqrt{a}-\sqrt{b}}\)

\(=\frac{a\left(\sqrt{a}-\sqrt{b}\right)+b\left(\sqrt{a}-\sqrt{b}\right)}{\sqrt{a}-\sqrt{b}}=a+b\)

Ta có: \(P=\frac{a\sqrt{b}+b\sqrt{a}}{\sqrt{a}+\sqrt{b}}-\frac{\sqrt{a^3}-\sqrt{a^2b}+\sqrt{ab^2}-\sqrt{b^3}}{\sqrt{a}-\sqrt{b}}\)

\(=\sqrt{ab}-a-b\)

b: \(P=-a+\sqrt{ab}-b\)

\(=-\left(a-\sqrt{ab}+b\right)=-\left(a-\sqrt{ab}+\frac14b+\frac34b\right)\)

\(=-\left(\sqrt{a}-\frac12\sqrt{b}\right)^2-\frac34b<0\forall a,b\) thỏa mãn ĐKXĐ

c: \(P=2\sqrt{ab}-b\)

=>\(\sqrt{ab}-a-b=2\sqrt{ab}-b\)

=>\(-a-\sqrt{ab}=0\)

=>\(a+\sqrt{ab}=0\)

=>\(\sqrt{a}\left(\sqrt{a}+\sqrt{b}\right)=0\) (vô lý vì a>0; b>0)

=>(a;b)∈∅

In the history and culture of Vietnam, women have always played a vital role. They are not only the "fire-keepers" of the family but also active contributors to society. There are three typical characteristics that define Vietnamese women: resilience, industriousness, and sacrifice.

Firstly, resilience is a hallmark of Vietnamese women. Throughout history, they have shown great courage in defending the country and overcoming hardships. In modern times, this strength is reflected in their ability to balance a professional career with household responsibilities. They stay strong and optimistic even when facing life's biggest challenges.

Secondly, Vietnamese women are well-known for being industrious and hard-working. Whether they are farmers in the countryside or office workers in the city, they always work with great diligence. They are famous for their "resourcefulness" (đảm đang), meaning they can manage money, housework, and childcare efficiently while still excelling at their jobs.

Lastly, sacrifice and devotion are deep-rooted qualities. For many Vietnamese women, the happiness of their family comes before their own. They spend most of their time and energy caring for their parents, husbands, and children. This selfless love is the glue that keeps Vietnamese families close-knit and stable across generations.

In conclusion, the combination of resilience, hard work, and a devoted heart makes Vietnamese women truly special. They continue to preserve traditional values while successfully adapting to the modern world, making them the pride of the nation.

II. Phần tự luận

Câu 1: Động năng của một vật phụu thuộc vào khối lượng và vận tốc

Ví dụ về vật vừa có động năng vừa có thế năng: một chiếc lá đang rơi từ trên cây xuống

Câu 2: Vì nếu cho đá vào trước thì đường và chanh sẽ chậm hòa tan vàotrong nước do nhiệt độ càn cao thì các hạt nguyên tử phân tử chuyển động càng nhanh nên cần hòa tan đường và chanh vào trước để được hòa tan vào trong nước hơn rồi mới nên cho đá vào

II. Phần tự luận:

Câu 3:

Công thực hiện được:

\(A=F.s=180.8=1440J\)

Công suất của người kéo:

\(\text{℘}=\dfrac{A}{t}=\dfrac{1440}{30}==48W\)

Câu 4:

Đổi: \(12km/h=43,2m/s\)

Công suất của ngựa:

\(\text{℘}=\dfrac{A}{t}=\dfrac{F.s}{t}=F.\dfrac{s}{t}=F.\upsilon=320.43,2=13824W\)

x + 3y = x(5y - 1)   (1)

1/x - 3/y = -2    (2)

(1) ⇔ x(5y - 1) - x = 3y

⇔ x(5y - 2) = 3y

⇔ x = 3y/(5y - 2)     (3)

Thế (3) vào (2) ta được:

(2) ⇔ 1/[3y/(5y - 2)] - 3/y = -2

⇔ (5y - 2)/3y - 3/y = -2

⇔ 5y - 2 - 9 = -6y

⇔ 5y + 6y = 11

⇔ 11y = 11

⇔ y = 1 thế vào (3) ta được:

x = 3.1/(5.1 - 2) = 1

Vậy S = {(1; 1)}

In my opinion, there are 3 typical characteristics of the Vietnamese people.

First, it’s saving money. They usually save money from their young age and until their old age. Nowadays, in the city, this view seems to change but those in countryside still share this point.The second outstanding feature is they live modestly and always work hard. In the past, they live mainly on farming, they wake up early in the morning and work all long day on the farm till the end of afternoon. They also don’t demand too much for their life, which you can be seen when seeing their houses and their customs. Until these modern days, they still have this habit.Besides, Vietnamese are actually friendly and hospitable people. Their hospitality is shown clearly in the way they greet and treat their friends and visitors. Either pre-arranged or unexpected, you always can receive a warm welcome by Vietnamese people because this is a part of their traditional culture.

Despite going through many ups and downs, basically, Vietnamese have still kept traditional values in their lifestyle reflected in the relationship of family and friends.