[tex]-x^{2} + 4x + 21=0\\[/tex]
Δ = [tex]b^{2} -4ac[/tex]
Δ = [tex]4^{2} - 4*-1*21= 16+4*21=16+84=100[/tex]
[tex]\sqrt{}[/tex] Δ = 10
x₁ = [tex]\frac{-b - \sqrt{} delta (ten trojkat)}{2a}[/tex]
x₁= [tex]\frac{-4-10}{-2}[/tex] = 7
x₂ = [tex]\frac{-4+10}{-2}[/tex] = -3
Odpowiedź:
[tex]-x^2+4x+21=0\\\\a=-1\ \ ,\ \ b=4\ \ ,\ \ c=21\\\\\Delta=b^2-4ac\\\\\Delta=4^2-4\cdot(-1)\cdot21=16+84=100\\\\\sqrt{\Delta}=\sqrt{100}=10\\\\\\x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-4-10}{2\cdot(-1)}=\frac{-14}{-2}=7\\\\x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-4+10}{2\cdot(-1)}=\frac{6}{-2}=-3[/tex]
