\(10+12=25-X\)

\(X=3\)

\(30-10=50-X\)

\(X=30\)

10 + 12 = 25 - x

22 = 25 - x

x = 3

30 - 10 = 50 - x

20 = 50 - x

x = 30

10+12=25-x

=>25-x=10+12

=>25-x=22

=>x=25-22

=>x=3

a) x - (-7) = -8 + (-2)

x + 7 = -8 - 2

x + 7 = -10

x = -10 - 7

x = -17

b) x + (12 - 15) = /-3/ - 7

x + (-3) = 3 - 7

x - 3 = -4

x = -4 + 3

x = -1

c) (12 - x) - (-10) = -25

(12 - x) + 10 = -25

12 - x = -25 - 10

12 - x = -35

x = 12 - (-35)

x = 12 + 35 = 47

d) (-20) - (15 - x) = -50

15 - x = -20 - (-50)

15 - x = -20 + 50

15 - x = -30

x = 15 - (-30)

x = 15 + 30

x = 45

( 2x + 1 / 2 ) * ( 3 / 4 - x ) = 0

=> 2x + 1 / 2 = 0 hoặc 3 / 4 - x = 0

               2x  = - 1 / 2             x = 3 / 4 

                 x  = - 1 / 4                

Vậy x = -1 / 4 hoặc x = 3 / 4

2 / 10 * 12 + 2 / 12 * 14 + 2 / 14 * 16 + ... + 2 / 48 * 50

= 1 / 10 - 1 / 12 + 1 / 12 - 1 / 14 + 1 / 14 + 1 / 16 + .... + 1 / 48 - 1/ 50

= 1 / 10 - 1 / 50 

= 2 / 25

Tìm x : \(\left(2x+\frac{1}{2}\right)\left(\frac{3}{4}-x\right)=0\)

\(\Rightarrow\orbr{\begin{cases}2x+\frac{1}{2}=0\\\frac{3}{4}-x=0\end{cases}\Rightarrow\orbr{\begin{cases}x=\frac{-1}{2}\\x=\frac{3}{4}\end{cases}}}\)

Tính nhanh : \(\frac{2}{10.12}+\frac{2}{12.14}+...+\frac{2}{48.50}\)

\(=2\left(\frac{1}{10.12}+\frac{1}{12.14}+...+\frac{1}{48.50}\right)\)

\(=2.\frac{1}{2}\left(\frac{1}{10}-\frac{1}{12}+\frac{1}{12}-\frac{1}{14}+...+\frac{1}{48}-\frac{1}{50}\right)\)

\(=\frac{1}{10}-\frac{1}{50}\)

\(=\frac{2}{25}\)

12 tấn 12 tạ = 10 800kg + 2400kg

7 tạ 80 kg = 15 600kg : 20

15 giờ < 16 phút x 60

12 giây x 50 > 9 phút 45 giây

#NgHn