x₁ + x₂ = - ( - 2m ) / 2 = m
ridicam la patrat ( x₁ + x₂ ) ² = m²
x₁² + 2x₁x₂ + x₂² =m²
produsul
x₁² + x₂² = m² - 2 ( 7 - 4m ) / 2 = m² - ( 7 - 4m ) = m² + 4m - 7
x₁x₂ = ( 7 - 4m ) / 2
= x₁² - 4x₁ + 4 + x₂² - 4x₂ + 4 = ( x₁² + x₂² ) - 4 ( x₁ + x₂ ) +8 =
inlocuim :
= m² + 4m - 7 - 4 ( m ) + 8 = m² + 4m - 7 - 4m + 8 = m² + 1 , adevarat