1)
x + 25x² + 20x + 4 = 25 + 50x + 25x²
50x - 21x = 4 - 25
29x = -21
x = -21/29
2)
16x² - 9 - 16x² + 2x = 0
2x = 9
x = 4,5
3)
3(x+5)² - 4x = 4 - x²
3x² + 30x + 75 - 4x = 4 - x²
4x² + 26x + 71 = 0
D = 676 - 1136 < 0 нет решений в R
4) x² - 1 = 2x² - 12x + 18 - x²
12x = 18 + 1
12x = 19
x = 19/12