2. Решите уравнения a) ((15-2(18:x+2))-18+9): 11 = 9 б)\frac{2}{5}x + x + 4x = \frac{9}{25}

2. Решите уравнения

a) $$((15-2(18:x+2))-18+9): 11 = 9$$

1. $$ (15-2(18:x+2))-18+9 = 9 \cdot 11 $$
2. $$ (15-2(18:x+2))-18+9 = 99 $$
3. $$ 15-2(18:x+2)-9 = 99 $$
4. $$ 15-2(18:x+2) = 108 $$
5. $$ -2(18:x+2) = 93 $$
6. $$ 18:x+2 = -46,5 $$
7. $$ 18:x = -48,5 $$
8. $$ x = 18:(-48,5) $$
9. $$ x = -\frac{180}{485} = -\frac{36}{97} $$

Ответ: $$x = -\frac{36}{97}$$

б) $$\frac{2}{5}x + x + 4x = \frac{9}{25}$$

1. $$\frac{2}{5}x + x + 4x = \frac{2x}{5} + \frac{5x}{5} + \frac{20x}{5} = \frac{27x}{5}$$
2. $$\frac{27x}{5} = \frac{9}{25}$$
3. $$x = \frac{9}{25} \cdot \frac{5}{27} = \frac{1}{5} \cdot \frac{1}{3} = \frac{1}{15}$$

Ответ: $$x = \frac{1}{15}$$