Question

resolva a equação X (x+3)=5x + 15

Answer 1

x(x+3) - 5x -15 = 0

x² + 3x - 5x - 15 = 0

x² - 2x - 15 = 0

Δ = 4 + 60
Δ = 64

x = 2 +-√64/2
x = 2 +-8/2

x' = 2+8/2
x' = 10/2 
x' = 5

x'' = 2-8/2
x'' = -6/2
x'' = -3                   S = { -3 , 5 }                   ok

Answer 2

x.(x + 3) = 5x + 15
x² + 3x = 5x + 15
x² + 3x - 5x - 15 = 0
x² - 2x - 15 = 0
a = 1; b = - 2; c = - 15
Δ = b² - 4ac
Δ = (-2)² - 4.1.(-15)
Δ = 4 - 4.(-15)
Δ = 4 + 60
Δ = 64

x = - b +/- √Δ  =  -  (-2) +/- √64
      --------------    -------------------
              2a                 2.1

x =  2 + 8  = 10/2 = 5
      --------
           2

x =  2 - 8    =  - 6/2 = - 3
      ---------
          2

R.: x = 5 e x = - 3