(x^2 + x + 1)(x^2 + x + 1) - 12 = 0; (x^2 + 2x)^2 + 9x^2 + 18x + 20 = 0; (x^2 + 8x + 7)(x + 3)(x + 4) + 15 = 0

a, (x^2 + x + 1)(x^2 + x + 1) - 12 = 0
b, (x^2 + 2x)^2 + 9x^2 + 18x + 20 = 0
c, (x^2 + 8x + 7)(x + 3)(x + 4) + 15 = 0