1262. Решите уравнение: 3) (20-1x) - 17,8 = 1; 4) 2/11 + (3,6x+1)= 5,1; 7) 42,21: (21x-7) = 14,07; 8) (x + 5,2): 1 = 8,1.

3) $$(20-1\frac{1}{3}x) - 17,8 = \frac{1}{5}$$

$$20 - 1\frac{1}{3}x = 17,8 + \frac{1}{5}$$

$$20 - 1\frac{1}{3}x = 17,8 + 0,2$$

$$20 - 1\frac{1}{3}x = 18$$

$$1\frac{1}{3}x = 20-18$$

$$1\frac{1}{3}x = 2$$

$$\frac{4}{3}x = 2$$

$$x = \frac{2 \cdot 3}{4} = \frac{3}{2} = 1,5$$

Ответ: 1,5

4) $$\frac{2}{11} + (3,6x+1\frac{7}{22})= 5,1$$

$$3,6x+1\frac{7}{22} = 5,1 - \frac{2}{11}$$

$$3,6x+1\frac{7}{22} = 5,1 - \frac{4}{22}$$

$$3,6x+1\frac{7}{22} = 5,1 - \frac{2}{11}$$

$$3,6x+1\frac{7}{22} = 5,1 - 0,(18)$$

$$3,6x+1\frac{7}{22} = 4,9(01)$$

$$3,6x = 4,9(01)-1\frac{7}{22}$$

$$3,6x = 4,9(01)-1,31(81)$$

$$3,6x = 3,582$$

$$x = \frac{3,582}{3,6} = 0,995$$

Ответ: 0,995

7) $$42,21: (21x-7) = 14,07$$

$$21x-7 = \frac{42,21}{14,07}$$

$$21x-7 = 3$$

$$21x=10$$

$$x=\frac{10}{21}$$

Ответ: $$\frac{10}{21}$$

8) $$\left(\frac{13}{21}x + 5,2\right): 1\frac{5}{21} = 8,1$$

$$\frac{13}{21}x + 5,2 = 8,1 \cdot 1\frac{5}{21}$$

$$\frac{13}{21}x + 5,2 = 8,1 \cdot \frac{26}{21}$$

$$\frac{13}{21}x + 5,2 = \frac{210,6}{21}$$

$$\frac{13}{21}x + 5,2 = 10,028$$

$$\frac{13}{21}x = 10,028 - 5,2$$

$$\frac{13}{21}x = 4,828$$

$$x = \frac{4,828 \cdot 21}{13} = \frac{101,388}{13} = 7,799$$

Ответ: 7,799