A

x² - 5x - 6 = 0

a = 1    b = - 5    c = - 6

delta = b² - 4ac

delta = (-5)² - 4 . 1 . (-6)

delta= 25 + 24

delta= 49

x = - b +- √Δ /2a

x = - (-5) +-  √ 49 /2.1

x = (5 + - 7)/2

x' = ( 5 + 7)/2   = 12/2  = 6

x'' = ( 5 - 7)/2   = - 2/2  = - 1

s= { -1  ; 6 }

B

x² - 2x - 15 = 0

a = 1  b = - 2 c = - 15

delta = b² - 4ac

delta = (-2)² - 4 . 1 . (-15)

delta = 4 + 60

delta = 64

x = - b +- √Δ /2a

x = - (-2) + - √ 64 /2.1

x = (2 +- 8) /2

x' = ( 2 + 8)/2  = 10/2  = 5

x'' = ( 2 - 8) /2  = - 6/2  = - 3

s = { -3 ; 5 }

C

6t² - 7t + 2 = 0

a = 6    b = - 7   c = 2

delta = b² - 4ac

delta = (-7)² - 4 . 6 . 2

delta = 49 - 48

delta = 1

x = - b +- √Δ /2a

x = - (-7) + - √1 / 2.6

x = (7 +- 1 ) /12  

x' = ( 7 + 1) /12  = 8/12 (simplifica por 4 ) = 2/3

x'' = ( 7 - 1)/12  = 6/12 ( simplica por 3 ) =  2/4

s = { 2/3 ; 2/4

D

3v² - 22v + 35 = 0

a = 3    b = - 22   c = 35

delta = b² - 4ac

delta = (-22)² - 4 . 3 . 35

delta = 484 - 420

delta = 64

x = - b +- √Δ /2a

x = - (-22) +- √64 /2.3

x = (22 +- 8) /6

x' = ( 22 + 8)/6  = 30/6  = 5

x'' = ( 22 - 8 ) /6  = 14/6 ( simplifica por 2 ) = 7/3

s = { 7/3 ; 5}