C
for the quadratic 2x² - x - 1 = 0 ← in standard form
with a = 2, b = - 1 and c = - 1 , then
x = (1 ± √( 1 + 8 )) / 4 ← quadratic formula
= ( 1 ± [tex]\sqrt{9}[/tex]) / 4
= ( 1 ± 3 ) / 4
x = [tex]\frac{1+3}{4}[/tex] or x = [tex]\frac{1-3}{4}[/tex]
x = [tex]\frac{4}{4}[/tex] = 1 or x = [tex]\frac{-2}{4}[/tex] = - [tex]\frac{1}{2}[/tex]
