Tìm x: 2x - 3 = 3 ( 2x -3 ) + x + 2

a, 2x - 3 = 3 ( 2x -3 ) + x + 2
b, x - 5x -1 / 6 = 8 - 3x / 4 
c, 5x /x^2 - 4 - 4 / x + 2 = 5 / x - 2 
 d, x^4 - 15x^2 + 56 = 0