Question

Х^2-3х-40=0 решите уравнение

Answer 1

х²-3х-40=0

х₁+х₂=3    -- теорема Виета
х₁х₂= - 40

х₁=8
х₂= - 5

$D=b^{2}-4ac \\ x_{1}= \frac{-b- \sqrt{D} }{2a} \\ x_{2}= \frac{-b +\sqrt{D} }{2a} \\ \\ D=(-3)^{2}-4* (-40)=9+160=169 \\ x_{1}= \frac{-(-3)- \sqrt{169} }{2*1} = \frac{3-13}{2}= \frac{-10}{2} =-5 \\ x_{2}= \frac{-(-3)+ \sqrt{169} }{2*1} = \frac{3+13}{2}= \frac{16}{2} =8$