28=2.2.7

12 = 2.2.3

em nhân   \(\sqrt{7}\)vào ngoặc  thì ra ... chỉ còn 7 thôi

em nhân phá ngoặc ra thôi 

Cái chỗ này mình xin lỗi bạn nhiều nha, mình bị sai chỗ này rồi

Ta có: \(\left(a-b\right)^2>=0\forall a,b\)

=>\(a^2+b^2-2ab>=0\forall a,b\)

=>\(a^2+b^2>=2ab\forall a,b\)

Dấu "=" xảy ra khi a=b

\(2\cdot\left(\dfrac{a}{2}\cdot\dfrac{b}{2}\right)< =\left(\dfrac{a}{2}\right)^2+\left(\dfrac{b}{2}\right)^2=\dfrac{a^2+b^2}{4}\)

=>\(2\cdot\left(2\cdot\dfrac{a}{2}\cdot\dfrac{b}{2}\right)< =\dfrac{2\left(a^2+b^2\right)}{4}=\dfrac{a^2+b^2}{2}\)

Bạn bỏ giúp mình dấu căn nha

bạn lớp mấy vậy?

=>5x^2-6x-11=0

=>5x^2-11x+5x-11=0

=>(5x-11)(x+1)=0

=>x=11/5 hoặc x=-1

Bài 1:

\(54\left(\dfrac{km}{h}\right)=15\left(\dfrac{m}{s}\right);9\left(\dfrac{m}{s}\right)=32,4\left(\dfrac{km}{h}\right)\)

Baì 2:

\(t'=s':v'=5:\left(5.3,6\right)=\dfrac{5}{18}h\)

\(\Rightarrow v_{tb}=\dfrac{s'+s''}{t'+t''}=\dfrac{5+3,8}{\dfrac{5}{18}+\left(\dfrac{15}{60}\right)}\simeq16,67\left(\dfrac{km}{h}\right)\)

Nhường e cái lý 8 với ạ :((

Câu 2: 

\(\Leftrightarrow\left(x+2\right)\left(10x+3\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x=-2\\x=-\dfrac{3}{10}\end{matrix}\right.\)

16. He told Min that he would meet her the following day / the next day.

17. Tom asked Linda if he could sit beside her.

18. He told his mom that he wanted a big cake for his birthday.

19. He told us not to turn the light on.

20. I asked him how long he was going to stay.

21. She wanted to know if Hoa was going by bike.

22. She asked us not to use too much hot water.

23. She invited me to come to her party.