Bài 3. Tìm x, biết: a) \( 3x(x+1) - (x-2)(3x+1) = 12 \) b) \( (3x^2 - x + 1)(x - 1) + x^2(4 - 3x) = \frac{5}{2} \) c) \( (x + 3)(5x - 1) = 5(x + 1)(x - 2) \) d) \( (2x - 3)(x + 1) = 2x(x - 1) \) e) \( \frac{1}{4} - \frac{1}{2} (x - 4) \cdot \frac{1}{2} x = -14 \) f) \( 3(1 - 4x)(x - 1) + 4(3x - 2)(x + 3) = -27 \)

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Bài 3.

Tìm x, biết:

a) \( 3x(x+1) - (x-2)(3x+1) = 12 \)

b) \( (3x^2 - x + 1)(x - 1) + x^2(4 - 3x) = \frac{5}{2} \)

c) \( (x + 3)(5x - 1) = 5(x + 1)(x - 2) \)

d) \( (2x - 3)(x + 1) = 2x(x - 1) \)

e) \( \frac{1}{4} - \frac{1}{2} (x - 4) \cdot \frac{1}{2} x = -14 \)

f) \( 3(1 - 4x)(x - 1) + 4(3x - 2)(x + 3) = -27 \)