Học sinh tự nhẩm và ghi như sau:

8 x 3 = 24

8 x 2 = 16

8 x 4 = 32

8 x 1 = 8

8 x 5 = 40

8 x 6 = 48

8 x 7 = 56

0 x 8 = 0

8 x 8 = 64

8 x 10 = 80

8 x 9 = 72

8 x 0 = 0

1.24

2.16

3.32

4.8

5.40

6.48

7.56

8.0

9.64

10.80

11.72

12.0

7 x 3 = 21

7 x 8 = 56

7 x 2 = 14

7 x 1 = 7

7 x 4 = 35

7 x 6 = 42

7 x 10 = 70

0 x 7 = 0

7 x 7 = 49

7 x 4 = 28

7 x 9 = 63

7 x 0 = 0

7x3=21

7x8=56

7x2=14

7x1=7

7x5=35

7x6=42

7x10=70

0x7=0

7x7=49

7x4=28

7x9=63

7x0=0

7 x 1 = 7

7 x 8 = 56

7 x 6 = 42

7 x 5 = 35

7x 2 = 14

7 x 9 = 63

7 x 4 = 28

0 x 7 = 0

7x 3 = 21

7 x 7 = 49

7 x 0 = 0

7 x 10 = 70

7 x 2 = 14       7 x 5 = 35       7 x 6 = 42       0 x 7 = 0

7 x 4 = 28       7 x 3 = 21       7 x 9 = 63       7 x 0 = 0

7 x 8 = 56       7 x 1 = 7       7 x 10 =70       1 x 7 = 7

mà đây là môn toán mà

55

Ta có : \(\left|2x+4\right|+\left|4x+8\right|=0\left|2x+4\right|+\left|4x+8\right|=0\)

\(\Rightarrow\left|2x+4\right|+2.\left|2x+4\right|=\left|4x+8\right|=0\)

\(\Rightarrow\left|2x+4\right|\left(1+2\right)=0\)

=> |2x + 4| = 0

=> 2x + 4 = 0

=> 2x = -4

=> x = -2

1. Đề đúng phải là thế này: \(\left|2x+4\right|+\left|4x+8\right|=0\)

\(\Rightarrow\left|2x+4\right|=\left|4x+8\right|=0\)

\(\Rightarrow2x+4=4x+8=0\)

\(\Rightarrow x=-\frac{4}{2}=-\frac{8}{4}\)

\(\Rightarrow x=-2\)

2. Sửa lại đề : \(\left|x-5\right|-\left|x-7\right|=0\)

\(\Rightarrow\left|x-5\right|=\left|x-7\right|\)

\(\Rightarrow\orbr{\begin{cases}x-5=x-7\\x-5=-\left(x-7\right)\end{cases}}\)

\(\Rightarrow\orbr{\begin{cases}-5=-7\\x-5=-x+7\end{cases}}\)

( Loại trường hợp 1)

\(\Rightarrow2x=12\)

\(\Rightarrow x=6\)

3.  \(\left|x+8\right|-\left|2x+2\right|=0\)

\(\Rightarrow\left|x+8\right|=\left|2x+2\right|\)

\(\Rightarrow\orbr{\begin{cases}x+8=2x+2\\x+8=-\left(2x+2\right)\end{cases}}\)

\(\Rightarrow\orbr{\begin{cases}x+2=8\\x+8=-2x-2\end{cases}}\)

\(\Rightarrow\orbr{\begin{cases}x=6\\3x=-10\end{cases}}\)

\(\Rightarrow\orbr{\begin{cases}x=6\\x=-\frac{10}{3}\end{cases}}\)

\(1,\Leftrightarrow x\left(x-9\right)=0\Leftrightarrow\left[{}\begin{matrix}x=9\\x=0\end{matrix}\right.\\ 2,\Leftrightarrow x^2-4x-x^2=7\Leftrightarrow-4x=7\Leftrightarrow x=-\dfrac{7}{4}\\ 3,\Leftrightarrow3x+2x-10=5\Leftrightarrow5x=15\Leftrightarrow x=3\\ 4,\Leftrightarrow\left(5x-1\right)\left(5x+1\right)=0\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{1}{5}\\x=-\dfrac{1}{5}\end{matrix}\right.\\ 5,\Leftrightarrow\left(x-2\right)\left(3x-5\right)=0\Leftrightarrow\left[{}\begin{matrix}x=2\\x=\dfrac{5}{3}\end{matrix}\right.\\ 6,\Leftrightarrow\left(x-7\right)\left(3x+4\right)=0\Leftrightarrow\left[{}\begin{matrix}x=7\\x=-\dfrac{4}{3}\end{matrix}\right.\)

\(7,\Leftrightarrow\left(2x-3\right)\left(2x+3\right)=0\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{3}{2}\\x=-\dfrac{3}{2}\end{matrix}\right.\\ 8,\Leftrightarrow\left(x-4\right)\left(10x+2\right)=0\Leftrightarrow\left[{}\begin{matrix}x=-\dfrac{1}{5}\\x=4\end{matrix}\right.\\ 9,\Leftrightarrow2x^2-5x-2x^2=0\Leftrightarrow x=0\\ 10,\Leftrightarrow2x\left(x-2\right)=0\Leftrightarrow\left[{}\begin{matrix}x=0\\x=2\end{matrix}\right.\\ 11,\Leftrightarrow\left(4x-3\right)\left(3-2x\right)=0\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{3}{4}\\x=\dfrac{3}{2}\end{matrix}\right.\\ 12,\Leftrightarrow2x^2-10x-2x^2=3\Leftrightarrow-10x=3\Leftrightarrow x=-\dfrac{3}{10}\)

\(1,\Leftrightarrow x\left(x-9\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}x=0\\x=9\end{matrix}\right.\\ 2,\Leftrightarrow x^2-4x-x^2=7\\ \Leftrightarrow-4x=7\\ \Leftrightarrow x=\dfrac{-7}{4}\\ 3,\Leftrightarrow3x+2x-10=5\\ \Leftrightarrow5x=15\\ \Leftrightarrow x=3\\ 4,\Leftrightarrow\left(5x-1\right)\left(5x+1\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}x=\dfrac{1}{5}\\x=-\dfrac{1}{5}\end{matrix}\right.\)

\(5,\Leftrightarrow\left(x-2\right)\left(3x-5\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}x=2\\x=\dfrac{5}{3}\end{matrix}\right.\\ 6,\Leftrightarrow\left(3x+4\right)\left(x-7\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}x=-\dfrac{4}{3}\\x=7\end{matrix}\right.\\ 7,\Leftrightarrow\left(2x-3\right)\left(2x+3\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}x=\dfrac{3}{2}\\x=-\dfrac{3}{2}\end{matrix}\right.\)

\(8,\Leftrightarrow10x\left(x-4\right)+2\left(x-4\right)=0\\ \Leftrightarrow\left(x-4\right)\left(10x+2\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}x=4\\x=-\dfrac{1}{5}\end{matrix}\right.\\ 9,\Leftrightarrow2x^2-5x-2x^2=0\\ \Leftrightarrow-5x=0\\ \Leftrightarrow x=0\\ 10,\Leftrightarrow2x\left(x-2\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}x=0\\x=2\end{matrix}\right.\)

\(11,\Leftrightarrow\left(2x-3\right)\left(4x-3\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}x=\dfrac{3}{2}\\x=\dfrac{3}{4}\end{matrix}\right.\\ 12,\Leftrightarrow2x^2-10x-2x^2=3\\ \Leftrightarrow-10x=3\\ \Leftrightarrow x=-\dfrac{3}{10}\)

1) \(x^2-9x=0\Rightarrow x\left(x-9\right)=0\Rightarrow x=0;9\)

2) \(x\left(x-4\right)-x^2=7\Rightarrow-4x=7\Rightarrow x=-\dfrac{7}{4}\)

3) \(3x+2\left(x-5\right)=5\Rightarrow5x-10=5\Rightarrow5x=15\Rightarrow x=3\)

4) \(25x^2-1=0\Rightarrow x^2=\dfrac{1}{25}\Rightarrow x=\pm\dfrac{1}{5}\)

5) \(3x\left(x-2\right)-5\left(x-2\right)=0\Rightarrow\left(x-2\right)\left(3x-5\right)=0\Rightarrow x=2;\dfrac{5}{3}\)

6) \(3x\left(x-7\right)+4\left(x-7\right)\Rightarrow\left(3x+4\right)\left(x-7\right)=0\Rightarrow x=-\dfrac{4}{3};7\)

7) \(4x^2-9=0\Rightarrow x^2=\dfrac{9}{4}\Rightarrow x=\pm\dfrac{3}{2}\)

8) \(10x\left(x-4\right)+2x-8=0\Rightarrow2\left(x-4\right)\left(5x+1\right)=0\Rightarrow x=4;-\dfrac{1}{5}\)

9) \(x\left(2x-5\right)-2x^2=0\Rightarrow x\left(2x-5-2x=0\right)\Rightarrow x=0\)

10) \(2x^2-4x=0\Rightarrow2x\left(x-2\right)=0\Rightarrow x=0;2\)

11) \(2x\left(3-4x\right)+3\left(4x-3\right)=0\Rightarrow2x\left(4x-3\right)-3\left(4x-3\right)=0\Rightarrow\left(4x-3\right)\left(2x-3\right)=0\Rightarrow x=\dfrac{3}{4};\dfrac{3}{2}\)

12) \(2x\left(x-5\right)-2x^2=3\Rightarrow-10x=3\Rightarrow x=-\dfrac{3}{10}\)

8 x 0 =0

8 x 8 =64

8 x 2 =16

8 x 4 =32

8 x 6 =48

8 x 9 =72

8 x 3 =24

8 x 7 =56

8 x 10 =80

8 x 0 =0

8 x 8 =64

8 x 2 =16

8 x 4 =32

8 x 6 =48

8 x 9 =72

8 x 3 =24

8 x 7 =56

8 x 10 =80

8 x 0 =0

8 x 8 =64

8 x 2 =16

8 x 4 =32

8 x 6 =48

8 x 9 =72

8 x 3 =24

8 x 7 =56

8 x 10 =80