Question

решите пожалуйста -4x²+21x-5=0

Answer 1

$- 4x^{2}+21x-5=0$
$D= b^{2}-4ac=21^{2}-4*(-4)*(-5)=441-80=361$
$x_{1}=frac{-b+sqrt{D}}{2a}=frac{-21+sqrt{361}}{-8}=frac{-21+19}{-8}=0,25$
$x_{2}=frac{-b-sqrt{D}}{2a}=frac{-21-sqrt{361}}{-8}=frac{-21-19}{-8}=5$