Câu 1:

\(\dfrac{3}{5}-\dfrac{5}{6}=\dfrac{18}{30}-\dfrac{25}{30}=\dfrac{18-25}{30}=\dfrac{-7}{30}\) 

Câu 2:

\(\dfrac{-5}{9}-\dfrac{-5}{12}=\dfrac{-20}{36}-\dfrac{-15}{36}=\dfrac{-20-\left(-15\right)}{36}=\dfrac{-5}{36}\)

 1. 3/5-5/6=-7/30

2.\(\dfrac{-5}{9}-\dfrac{-5}{12}=\dfrac{-5}{36}\)

Câu 1: \(1\dfrac{3}{5}-\dfrac{5}{6}=\dfrac{8}{5}-\dfrac{5}{6}=\dfrac{23}{30}\)

Câu 2: \(\dfrac{-5}{9}-\left(\dfrac{-5}{12}\right)=\dfrac{-5}{36}\)

Bài 8:

a: Ta có: \(\sqrt{4x}=\sqrt{5}\)

\(\Leftrightarrow4x=5\)

hay \(x=\dfrac{5}{4}\)

b: Ta có: \(\sqrt{4\cdot\left(1-x\right)^2}-6=0\)

\(\Leftrightarrow2\left|x-1\right|=6\)

\(\Leftrightarrow\left|x-1\right|=3\)

\(\Leftrightarrow\left[{}\begin{matrix}x-1=3\\x-1=-3\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=4\\x=-2\end{matrix}\right.\)

c: Ta có: \(\sqrt{2x-3}=\sqrt{7}\)

\(\Leftrightarrow2x-3=7\)

hay x=5

d: Ta có: \(\sqrt{\left(3x-2\right)^2}=4\)

\(\Leftrightarrow\left|3x-2\right|=4\)

\(\Leftrightarrow\left[{}\begin{matrix}3x-2=4\\3x-2=-4\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}3x=6\\3x=-2\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=2\\x=-\dfrac{2}{3}\end{matrix}\right.\)

Câu 8:

Ta có: \(n_{CO_2}=\dfrac{4,48}{22,4}=0,2\left(mol\right)\)

\(n_{H_2O}=\dfrac{5,4}{18}=0,3\left(mol\right)\)

BTNT O, có: \(2n_{O_2}=2n_{CO_2}+n_{H_2O}\)

\(\Rightarrow n_{O_2}=0,35\left(mol\right)\)

\(\Rightarrow V_{O_2}=0,35.22,4=7,84\left(l\right)\)

→ Đáp án: C

Câu 9: C

Bài 6 :

Vận tốc khi lên đèo :

\(v=\dfrac{s}{t}=\dfrac{45}{2,5}=18\left(\dfrac{km}{h}\right)\)

Vận tốc khi xuống đèo :

\(v=\dfrac{s}{t}=\dfrac{30}{0,5}=60\left(\dfrac{km}{h}\right)\)

Vận tốc tb : 

\(v_{tb}=\dfrac{s_1+s_2}{t_1+t_2}=\dfrac{45+30}{2,5+0,5}=25\left(\dfrac{km}{h}\right)\)

Bài 9:

b: Tọa độ giao điểm là:

\(\left\{{}\begin{matrix}2x-3=-3x+7\\y=2x-3\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=2\\y=1\end{matrix}\right.\)

2/6;3/6;4/6;5/6;6/6.

OK nhé bạn 

Nhầm chỗ,đúng thì là:

7/6;8/6;9/6;10/6.

Bây giờ mới ok 

7/6;8/6;9/6;10/6;11/6

bạn Mai làm thiếu phân số 11/6

---------CHÚC BẠN HỌC TỐT----------

1+2+3+4+5+6+7+8+9=45

1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 = (9 + 1) + (8 + 2) + (7 + 3) + (6 + 4) + 5

= 10 + 10 + 10 + 10 + 5 = 45

= 45 bạn nhé !