Решительно уравнение (2х+3)^2=(-х-7)^2

4x^2 + 12x + 9  = x^2 + 14x + 49
4x^2 + 12x + 9  - x^2 - 14x - 49 =  0
3x^2 - 2x - 40 = 0 
D = 4 + 4*3*40 = 4 + 480 = 484 = 22^2
x₁ = ( 2 + 22)/6 = 24/6 = 4;
x₂ = ( 2 - 22)/6 = - 20/6 = - 10/3 = - 3 целых 1/3