Решите систему уравнений 1/3x+1/4y=3,3x-2y=10

1) (x+1)² (x² + 2x) = 12
(x² + 2x + 1) (x² + 2x) = 12
x² + 2x = t
(t+1) t = 12
t² + t - 12 = 0
D = 1+48 = 49
t₁ = 3
t₂ = -4
x² + 2x = 3
x² + 2x - 3 = 0
x₁ = 1
x₂ = -3
x² + 2x = -4
x² + 2x + 4 =0
D = 4-16 <0
нет корней
ответ: 1; -3
2) x²  +3x = t
(t+1) (t+3) = -1
t² + 3t + t + 3 = -1
t² + 4t + 4 = 0
D₁ = 4-4 = 0
t = -2
x²  +3x = -2
x² + 3x + 2=0
x₁ = -1
x₂ = -2
ответ: -1; -2
3) x² - 4x = t
(t+1) (t+2) = 12
t² + 2t + t + 2 = 12
t² + 3t - 10 = 0
D = 9 + 40 = 49
t₁ = (-3+7) / 2 = 2
t₂ = (-3-7) / 2 = -5
x² - 4x = 2
x² - 4x - 2 = 0
D₁ = 4+2 = 6
x₁ = 2+√6
x₂ = 2-√6
x² - 4x = -5
x² - 4x + 5 = 0
D₁ = 4 - 5 < 0
нет корней
ответ: 2+√6 ; 2-√6

1) 

5x² = 0 или x-4=0
x = 0 или x=4
2) 9x - x³ = 0
x(9 - x²) = 0
x= 0 или 9 - x² = 0
x = 0 или x² = 9 ⇒ x= -3 или x= 3
ответ: -3, 0, 3
3) x³ + 3x² - 4x - 12 = 0 
(x³ + 3x²) - (4x + 12) = 0
x²(x + 3) - 4(x + 3) = 0
(x² - 4)(x + 3) = 0
x² - 4 = 0 или x+3 = 0
x=2 или x=-2 или x=-3
4) x³ - 2x² = 0 
x^2(x - 2) = 0
x = 0 или x=2
5) 9x² - 0.25 = 0
9x² = 0.25
x² = 1/36
x = 1/6 или x=-1/6
6) 64 - 9x² = 0
9x² = 64
x² = 64/9
x = 8/3 или x= - 8/3
7) 2x³ - x² - 18x + 9 = 0
(2x³ - x²) - (18x - 9) = 0
x²(2x - 1) - 9(2x - 1) = 0
(x² - 9)(2x - 1) = 0
x²=9 или 2x - 1 = 0
x = -3 или x= 3 или x = 1/2
8) x² - 6x + 9 = 0
(x - 3)² = 0
x - 3 = 0
x = 3
9) x²+10x+25=0
(x + 5)² = 0
x + 5 = 0
x = -5
10) 4x² - 4x + 1 = 0
(2x - 1)² = 0
2x - 1 = 0
2x = 1
x = 1/2
11) 9x²+6x+1=0
(3x + 1)² = 0
3x +1 = 0
x = -1/3
12) 3x - 0.4x²=0
x(3 - 0.4x) = 0
x = 0 или 3-0.4x = 0 ⇒ (2/5)x = 3 ⇒ x = 15/2 = 7.5
13) -0.4x² + 8x = 0
x( 8 - 0.4x) = 0
x = 0 или 0,4x = 8 ⇒ x = 20