[tex]x_{v} =\frac{-b}{2a} =\frac{-20}{2\cdotp ( -10)} \Longrightarrow \boxed{x_{v} =1} \\ \\ y_{v} \Leftrightarrow f( x_{v}) =f( 1) = \\ =-10\cdotp 1^{2} +20\cdotp 1-40\Longrightarrow \boxed{y_{v} =-30} \\ \\ \therefore \boxed{\boxed{V( 1,-30)}}[/tex]
