Question

achar raizes das equações

x²-x-20=0

x²-3x-4=0

x²-8x+7=0

Answer 1

x²-x-20=0

a=1, b= -1, c= - 20

∆ = b² – 4 * a * c
∆ = (-1)² – 4 * 1 * (–20)
∆ = 1+ 80
∆ = 81

x = – b ± √∆
         2∙a

x = –(-1) ± √81
         2∙1

x = 1 ± 9
         2

x'= 1 + 9 = x'=5
         2

x''= 1 - 9 =x"= - 4
         2
__________________________
x²-3x-4=0

a=1, b= -3, c= - 4

∆ = b² – 4 * a * c
∆ = (-3)² – 4 * 1 * (–4)
∆ = 9+16
∆ = 25

x = – b ± √∆
         2∙a

x = –(-3) ± √25
         2∙1

x = 3 ± 5
         2

x'= 3 +5= x'=4
         2

x''= 3 - 5= x''= - 1
         2
____________________________
x²-8x+7=0

a=1, b= -8, c= 7

∆ = b² – 4 * a * c
∆ = (-8)² – 4 * 1 *7
∆ = 64-28
∆ = 36

x = – b ± √∆
         2∙a

x = –(-8) ± √36
         2∙1

x = 8± 6
         2

x'= 8 + 6 = x'=7
         2

x''= 8 - 6 = x"= 1
         2