3. (x + 4) = 21; 5. (x-2) = 15; 2. (7 + x) = 20; • 4. (x - 3) = 16. 7. x + (2 + x) = 12 8. 15-(x + 1) = x + 4 9. (x + 10) - 5 = 2x 10. 20-(x-2) = 22

Решим уравнения: 1) 3(x + 4) = 21 3x + 12 = 21 3x = 21 - 12 3x = 9 x = 9 / 3 x = 3 2) 5(x - 2) = 15 5x - 10 = 15 5x = 15 + 10 5x = 25 x = 25 / 5 x = 5 3) 2(7 + x) = 20 14 + 2x = 20 2x = 20 - 14 2x = 6 x = 6 / 2 x = 3 4) 4(x - 3) = 16 4x - 12 = 16 4x = 16 + 12 4x = 28 x = 28 / 4 x = 7 5) x + (2 + x) = 12 x + 2 + x = 12 2x + 2 = 12 2x = 12 - 2 2x = 10 x = 10 / 2 x = 5 6) 15 - (x + 1) = x + 4 15 - x - 1 = x + 4 14 - x = x + 4 14 - 4 = x + x 10 = 2x x = 10 / 2 x = 5 7) (x + 10) - 5 = 2x x + 10 - 5 = 2x x + 5 = 2x 5 = 2x - x 5 = x x = 5 8) 20 - (x - 2) = 22 20 - x + 2 = 22 22 - x = 22 -x = 22 - 22 -x = 0 x = 0

Ответ: x = 3; x = 5; x = 3; x = 7; x = 5; x = 5; x = 5; x = 0

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