7) 5t² - 3 = 77
5t² = 77+ 3
5t² = 80
t² = 80:5
t² = 16
t1 = 4
t2 = -4
8) 1/2 x² = 8/9
x² = 8/9 : 1/2
x² = 8/9 * 2
x² = 16/9
x1 = 4/3 = 1 1/3
x2 = -4/3 = -1 1/3
5) y² - 2y - 8 = 2y - 8
y² - 2y - 2y = 0
y² - 4y = 0
y(y - 4) = 0
y1 = 0 y - 4 = 0
y2 = 4
6) 3u² + 7 = 6u + 7
3u² - 6u = 0
3u(u - 2) = 0
3u = 0 u - 2 = 0
u1 = 0 u = 2
8) (x - 3)(3x + 2) = (5x - 4)(3x - 2)
3x² + 2x - 9x - 6 = 15x² - 10x - 12x + 8
3x² - 15x² - 7x + 22x - 6 - 8 = 0
-12x² + 15x -14 = 0
D = b² - 4ac
D = 15² - 4*(-12)*(-14) = 225 - 672 = - 447 нет решения