2x^2-72=0
x^2=36
x = +-6
8x^2-5x-3=0
(8x+3)(x-1) = 0
x=1
x= -3/8 = -0,375
или
8x^2-5x-3=0
D = b^2-4ac
D = 25+96=121, √D = 11
x= (-b+-√D)/2a
x1 = (5+11)/16 = 1
x2 = (5-11)/16 = -0.375
16-8a^2=0
8a^2=16
a^2=2
a=+-√2
2a^2+3a+1=0
D = 1
x1=(-3+1)/4 = -0.5
x2=(-3-1)/4=-1
x^2+3x-18=0
D=81
x1=(-3+9)/2=3
x2=(-3-9)/2=-6
9x^2+12x+4 = 0
(3x+2)^2=0
x=-2/3
2x^2+7x+3=0
D = 25
x1=(-7+5)/4=-0.5
x2=(-7-5)/4=-3
15x^2-16x+4=0
D/4 = (b/2)^2-ac
D/4 = 16-60
D/4 < 0,
нет действительных корней