kho qua

515 – 415 = 100

Học sinh nhẩm và ghi kết quả như sau:

100 – 50 = 50

950 – 50 =900

515 – 415 =100

Mình làm 5 câu thôi nhé !:
1) \(7^x\cdot49=7^{90}\)

\(\Rightarrow7^x\cdot7^2=7^{90}\)

\(\Rightarrow7^{x+2}=7^{90}\)

\(\Rightarrow x=90-2\)

\(\Rightarrow x=88\)

2) \(2^x\cdot4=128\)

\(\Rightarrow2^x\cdot2^2=2^7\)

\(\Rightarrow2^{x+2}=2^7\)

\(\Rightarrow x=7-2\)

\(\Rightarrow x=5\)

3) \(3^x-1=2^4\cdot5\)

\(\Rightarrow3^x=80+1\)

\(\Rightarrow3^x=81\)

\(\Rightarrow3^x=3^4\)

\(\Rightarrow x=4\)

4) \(3^x+15=42\)

\(\Rightarrow3^x=42-15\)

\(\Rightarrow3^x=27\)

\(\Rightarrow3^x=3^3\)

\(\Rightarrow x=3\)

5) \(4\cdot2^x-3=125\)

\(\Rightarrow2^2\cdot2^x=128\)

\(\Rightarrow2^{x+2}=2^7\)

\(\Rightarrow x=7-2\)

\(\Rightarrow x=5\)

6) 

\(5^x=5^{15}:5^3\\ \Leftrightarrow5^x=5^{15-3}\\ \Leftrightarrow5^x=5^{12}\\ \Leftrightarrow x=12\)

7) 

\(4^x=4^{15}:16\\ \Leftrightarrow4^x=4^{15}:4^2\\ \Leftrightarrow4^x=4^{15-2}\\ 4^x=4^{13}\\ \Leftrightarrow x=13\)

8) 

\(7^x=7^{20}:7^{10}\\ \Leftrightarrow7^x=7^{20-10}\\ \Leftrightarrow7^x=7^{10}\\ \Leftrightarrow x=10\)

9) 

\(11^x=11^{11}:11\\ \Leftrightarrow11^x=11^{11-1}\\ \Leftrightarrow11^x=11^{10}\\ \Leftrightarrow x=10\)

10)

\(3^{15}.3^x=3^{30}\\ \Leftrightarrow3^x=3^{30}:3^{15}\\ 3^x=3^{30-15}\\ \Leftrightarrow3^x=3^{15}\\ \Leftrightarrow x=15\)

11)

\(10+2x=4^5:4^3\\ \Leftrightarrow10+2x=4^2\\ \Leftrightarrow2x=6\\ \Leftrightarrow x=3\)

12)

\(20+5x=5^5:5^3\\ \Leftrightarrow20+5x=5^2\\ \Leftrightarrow5x=5\\ \Leftrightarrow x=1\)

13)

\(4x-20=2^5:2^2\\ \Leftrightarrow4x-20=2^3\\ \Leftrightarrow4x=28\\ \Leftrightarrow x=12\)

14)

\(15+2x=3^{80}:3^{77}\\ \Leftrightarrow15+2x=3^3\\ \Leftrightarrow2x=12\\ \Leftrightarrow x=6\)

1. a) 4.415.8.25.125

= (4.25). (8.125).415

= 100.1000.415

= 100000.415

= 41500000

b) 2.31.12+4.42.6+8.27.3

= (2.31.12)+(4.42.6)+(8.27.3)

= (2.12).31+(4.6).42+(8.3).27

= 24.31+24.42+24.27

= 24 (31+42+27)

= 24.100

= 2400

a: =>4x-10=2x+4

=>2x=14

hay x=7

b: =>15x=3

hay x=1/5

1. 3x - 17 = x+3

    3x - x = 3 + 17

    2x      = 20

      x      = 20 :2

      x      = 10

2.  |x-3| - 12 = |-5|

     |x-3| -12  = 5

     |x-3|       =  5 + 12

     |x-3|       = 17

=> x-3 = +17 , -17

             x      = 17 + 3

             x      = 20

            x       =  -17 + 3

            x       = -14

3 . 25 - ( x -5 )  = -415 -( 15 -415)

     25 - x +5     =  -415 - 15 +415

     25 - x +5      =  ( -415 + 415) -15 

     25 - x +5     =    0-5 = -5

     25 - x          =    -5-5

     25 - x          = -10

           x           =  25 - -10

           x           =  35

4.  ( x -3 ) . ( 2x +6 ) = 0

=> x-3 = 0 hoặc 2x +6 = 0

           x      = 0 + 3 = 3

          2x      =  0-6=-6

           x       =  -6 : 2

           x       = -3

\(1;3x-17=x+3\)

\(\Leftrightarrow3x-x=3+17\)

\(\Leftrightarrow2x=20\)

\(\Rightarrow x=10\)

\(2;\left|x-3\right|-12=\left|-5\right|\)

\(\Leftrightarrow\left|x-3\right|-12=5\)

\(\Leftrightarrow\left|x-3\right|=5+12\)

\(\Leftrightarrow\left|x-3\right|=17\)

\(\Rightarrow\orbr{\begin{cases}x-3=17\\3-x=17\end{cases}\Leftrightarrow}\orbr{\begin{cases}x=17+3\\-x=17-3\end{cases}\Leftrightarrow\orbr{\begin{cases}x=20\\x=-14\end{cases}}}\)

\(3;25-\left(x-5\right)=-415-\left(15-415\right)\)

\(\Leftrightarrow25-x+5=-415-15+415\)

\(\Leftrightarrow-x=-415-15+415-25-5\)

\(\Leftrightarrow-x=-45\)

\(\Rightarrow x=45\)

\(4;\left(x-3\right)\left(2x+6\right)=0\)

\(\Rightarrow\orbr{\begin{cases}x-3=0\\2x+6=0\end{cases}\Leftrightarrow\orbr{\begin{cases}x=3\\x=-3\end{cases}}}\)

3x-17=x+3

3x-x=3+17

2x=20

x=10

lx-3l - 12 = l-5l = 5

lx-3l = 5+12=17

<=>\(\orbr{\begin{cases}x-3=17\\x-3=-17\end{cases}\Leftrightarrow\orbr{\begin{cases}x=20\\x=-14\end{cases}}}\)