a. -2x(x³ - 3x² - x + 1)

= -2x⁴ + 6x³ + 2x² - 2x

c. 3x²(2x³ - x + 5)

= 6x⁵ - 3x³ + 15x²

Bài 3: 

a: Ta có: \(6x\left(5x-3\right)+3x\left(1-10x\right)=7\)

\(\Leftrightarrow30x^2-18x+3x-30x^2=7\)

\(\Leftrightarrow x=-\dfrac{7}{15}\)

b: Ta có: \(3x\left(12x-4\right)-9x\left(4x-3\right)=30\)

\(\Leftrightarrow36x^2-12x-36x^2+27x=30\)

hay x=2

c: ta có: \(x\left(5-2x\right)-2x\cdot\left(x-1\right)=15\)

\(\Leftrightarrow5x-2x^2-2x^2+2x-15=0\)

\(\Leftrightarrow-4x^2+7x-15=0\)

\(\text{Δ}=7^2-4\cdot\left(-4\right)\cdot\left(-15\right)=-191\)

Vì Δ<0 nên phương trình vô nghiệm 

Trời trời giúp mình với mấy thần đồng tiếng anh ơi , mình sắp toang ròi 😢😢😢

chia nhỏ ra đi bn

TUI NÈ BẠN

Hello

An: Hello Manh , What are you doing ?

Manh : Oh , Hi An . I'm reading a magazine about tsunami .

An : What is tsunami ?

Manh : Tsunamis are giant waves caused by earthquakes or volcanic eruptions under the sea. Out in the depths of the ocean, tsunami waves do not dramatically increase in height. But as the waves travel inland, they build up to higher and higher heights as the depth of the ocean decreases. The speed of tsunami waves depends on ocean depth rather than the distance from the source of the wave. Tsunami waves may travel as fast as jet planes over deep waters, only slowing down when reaching shallow waters. While tsunamis are often referred to as tidal waves, this name is discouraged by oceanographers because tides have little to do with these giant waves.

An : It sounds terrible .What is it cause ?

Manh: First , it causes many deaths . Since 1850 alone, tsunamis have been responsible for the loss of more than 430,000 lives. Second , the amount of energy and water contained in a huge tsunami can cause extreme destruction when it strikes land. And finally Tsunamis not only destroy human life, but have a devastating effect on insects, animals, plants, and natural resources. A tsunami changes the landscape. It uproots trees and plants and destroys animal habitats such as nesting sites for birds. Land animals are killed by drowning and sea animals are killed by pollution if dangerous chemicals are washed away into the sea, thus poisoning the marine life.

An : How can we to stop it ?

Manh : From my point of view, we need many factors to simulate Tsunami wave than we can find solution for this problem. One of this factor as Gobo A.E. mentioned above, also we need to know how many cycle per each period for example 10 years that happened and also the height of the wave when it attach the land. When we study deeply all factors then we can find solution such as we can made some gates in front of the coast lying horizontal in water when the level of water increase more then the normal this gate change its position to the vertical to crash the wave height and to reduce the damage on the land behind it.

An : That's true.

Ảnh không phù hợp với học sinh. 

782392964x9=7041536676

k cho mình nha mình mới zo k 1 cái coi như điểm lần đầu thanks

1: =>x^2-5x+6-x^2-5x-6=x^2+1-x^2+9

=>-10x=10

=>x=-1(nhận)

2: \(\Leftrightarrow3x^2-15x-x^2+2x-2x^2=0\)

=>-13x=0

=>x=0

3: \(\Leftrightarrow13\left(x+3\right)+x^2-9=12x+42\)

=>x^2-9+13x+39-12x-42=0

=>x^2+x-12=0

=>(x+4)(x-3)=0

=>x=3(loại) hoặc x=-4(nhận)

4: \(\Leftrightarrow-2+x^2-5x+4=x^2+x-6\)

=>-5x-2=x-6

=>-6x=-4

=>x=2/3

Đúng rồi nhé bạn