Explicação passo-a-passo:

a) x² +2x - 3= 0

∆= 2²- 4.1.(-3)

∆= 4 +12

∆= 16

x= - 2 ±√16/2.1

x = - 2 ±4/2

x1 = -2+4/2= 2/2= 1

x2= -2-4/2= - 6/2= -3

S = { 1, -3}

b) x² - 5x +10 -4= 0

x ² -5x + 6= 0

∆= (-5)² - 4.1.6

∆= 25 - 24

∆= 1

x = - (-5) ±√1/2.1

x = 5 ±1/2

x1= 5+1/2=6/2= 3

x2= 5-1/2= 4/2= 2

S = { 3, 2}

c) 8x² - 2x - 21= 0

∆= (-2)² - 4.8.(-21)

∆= 4 + 672

∆= 676

x= - (-2) ±√676/2.8

x = 2 ±26/16

x1= 2+26/16 = 28/16= 13/8

x2= 2-26/16= - 24/16= - 12/8

S = { 13/8 , - 12/8{