Question

Calculati 72=(x+7)(x+1)

Answer 1

72 = (x + 7)(x + 1)

x² + 7x + x + 7 - 72 = 0
x² + 8x - 65 = 0
x² - 5x + 13x - 65 = 0           L-am descompus pe 8x in - 5x + 13x
x(x - 5) + 13(x - 5) = 0
(x - 5)(x + 13) = 0

x₁ = 5
x₂ = - 13

Se poate face si folosind discriminantul  Δ = b² - 4ac 

 

Answer 2

72=x^2+x+7x+7
72=x^2+8x+7
x^2+8x+7-72=0
x^2+8x-65=0
De unde aplicam delta
Δ=b²-4ac
  =8²-4·1·(-65)
  =64+260
  =324
  =18²
x₁,₂ =-b plus minus√Δ supra 2a
      =-8 plus minus 18 supra 2
 x₁=10 supra 2 =5
 x₂=-26 supra 2=-13