\(1,\\ a,=6x^4y^4-x^3y^3+\dfrac{1}{2}x^4y^2\\ b,=4x^3+5x^2-8x^2-10x+12x+15\\ =4x^3-3x^2+2x+15\\ 2,\\ a,=7\left(x^2-6x+9\right)=7\left(x-3\right)^2\\ b,=\left(x-y\right)^2-36=\left(x-y-6\right)\left(x-y+6\right)\\ 3,\\ \Leftrightarrow x\left(x^2-0,36\right)=0\\ \Leftrightarrow x\left(x-0,6\right)\left(x+0,6\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}x=0\\x=0,6\\x=-0,6\end{matrix}\right.\)

4 D

5 A

6 A

7 A

8 D

8 D

10 B

II

1 C

2A

3A

4B

5A

III

1 A

2 B

3 C

4 B

5 C

6 B

7 A

8 C

9 D

10 C

11 A

12 B

13 C

14 A

15 B

16 C

17 C

18 B

19 A

20 B

21 C

22 A

23 D

24 D

25 D

26 A

27 A

28 C

29 B

30 B

31 A

32 D

33 B

34 B

35 C

36 C

37 B

38 D

39 A

40 B

41 C

42 A

ab = a : b

a+m/b+m = (a + m) : (b + m)

a+m/b+m >a /b

Ta có: \(3x=4y\Rightarrow\dfrac{x}{4}=\dfrac{y}{3}\Rightarrow\dfrac{x}{20}=\dfrac{y}{15}\)

            \(2y=5z\Rightarrow\dfrac{y}{5}=\dfrac{z}{2}\Rightarrow\dfrac{y}{15}=\dfrac{z}{6}\)

Áp dụng t/c dtsbn:

\(\dfrac{x}{20}=\dfrac{y}{15}=\dfrac{z}{6}=\dfrac{x+z}{20+6}=\dfrac{52}{26}=2\)

\(\Rightarrow\left\{{}\begin{matrix}x=20.2=40\\y=15.2=30\\z=6.2=12\end{matrix}\right.\)