a) `4x^2+2x-1=0`
`-> (x-(1-\sqrt5)/4)(x-(1+\sqrt5)/4)=0`
`->` \(\left[ \begin{array}{l}x=\dfrac{1-\sqrt5}{4}\\x=\dfrac{1+\sqrt5}{4}\end{array} \right.\)
b) `4x^2+2x-1`
`->(2x)^2+2.2x . 1/2 + (1/2)^2 -5/4 `
`-> (2x+1/2)^2 -5/4 `
Vì `(2x+1/2)^2>=0 forall x => A_(min) = -5/4 <=> 2x+1/2 =0<=> x=-1/4`