Решите уравнение пожалуйста (x^2+6x)^2+2(x+3)^2=81

1. ( x^2 + 6x )^2 + 2( x + 3)^2 = 81;2. ( x^2 + 6x )^2 + 2( x^2 + 6x + 9 ) = 81;3. Пусть x^2 + 6x = t, тогда:t^2 + 2( t + 9 ) = 81;t^2 + 2t + 18 - 81 = 0;t^2 + 2t - 63 = 0;D = 4 + 252 = 256 = 16^2;t1 = ( -2 - 16 ) / 2 = -9;t2 = ( -2 + 16 ) / 2= 7;4. x^2 + 6x = -9;x^2 + 6x + 9 = 0;( x + 3 )^2 = 0;x = -3;5. x^2 + 6x = 7;x^2 + 6x - 7 = 0;D= 36 + 28 = 64 = 8^2;x1 = ( -6 - 8 ) /2 = -7;x2= ( -6 + 8 ) /2 = 1;6. Ответ: x = -3; x = 1; x = -7.