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a: =-3/7-5/9+3/7=-5/9

b: \(=\dfrac{5}{7}\left(\dfrac{2}{11}+\dfrac{3}{11}-\dfrac{16}{11}\right)=\dfrac{-5}{7}\)

c: \(=\dfrac{5}{4}-\dfrac{1}{4}\cdot\dfrac{-16}{3}+1=\dfrac{9}{4}+\dfrac{4}{3}=\dfrac{43}{12}\)

\(a^3+b^3+c^3=3abc\)

=>\(\left(a+b\right)^3+c^3-3ab\left(a+b\right)-3abc=0\)

=>\(\left(a+b+c\right)\left[\left(a+b\right)^2-c\left(a+b\right)+c^2\right]-3ab\left(a+b+c\right)=0\)

=>\(\left(a+b+c\right)\left(a^2+2ab+b^2-ac-bc+c^2-3ab\right)=0\)

=>\(a^2+b^2+c^2-ab-ac-bc=0\)

=>\(2a^2+2b^2+2c^2-2ab-2ac-2bc=0\)

=>\(\left(a^2-2ba+b^2\right)+\left(b^2-2cb+c^2\right)+\left(a^2-2ac+c^2\right)=0\)

=>\(\left(a-b\right)^2+\left(b-c\right)^2+\left(a-c\right)^2=0\)

=>\(\left\{{}\begin{matrix}a-b=0\\b-c=0\\a-c=0\end{matrix}\right.\Leftrightarrow a=b=c\)

\(A=\dfrac{a^{2023}}{b^{2023}}+\dfrac{b^{2023}}{c^{2023}}+\dfrac{c^{2023}}{a^{2023}}\)

\(=\dfrac{a^{2023}}{a^{2023}}+\dfrac{b^{2023}}{b^{2023}}+\dfrac{c^{2023}}{c^{2023}}\)

=1+1+1

=3

4:

A=8a^2-10ab-b^2-6a^2+2ab-b^2-a^2+8ab-4b^2

=a^2-6b^2

Khi a=-1 và b=4a^2-2=4-2=2 thì

A=(-1)^2-6*2^2

=1-24=-23

Sau ngày 1 còn 1-2/5=3/5

Sau ngày 2 còn 3/5*1/3=3/15=1/5

Quyển sách có 50:1/5=250(trang)

Em cảm ơn nhiều ạ!

mai's team performed less successful than lan's team

Cars go less slowly than motorbikes

The broken cup is hidden in the drawer  

Some cups of tea were bought to the visitors in the next room

33 Mai's team performed less successfully than Lan's team

34 Cars go faster than Motorbikes 

35 The broken cup is hidden in the drawer by him

36 Some cups of tea were bought to the visitors in the next room

Trắc nghiệm :

1. A

2.C

3.A

4.B

5.A

Chị=20

Em = 12

Cảm ơn nhé