Question

Calculate the discriminant x2-2x+4=0 A.0 B.20 C.12 D.-12

Answer 1

$x^2-2x+4=0 \\ \\ a=1 \\ b=-2 \\ c=4 \\ \\ \hbox{the discriminant: } \Delta=b^2-4ac=(-2)^2 - 4 \times1 \times 4=4-16=-12$

The answer is D.

Answer 2

$ax^2+bx+c=0\\the\ discriminant:\Delta=b^2-4ac\\-------------------\\Your\ example:\\x^2-2x+4=0\to a=1;\ b=-2;\ c=4\\\\thereore\ \Delta=(-2)^2-4\cdot1\cdot4=4-16=\fbox{-12}\\\\Answer:\boxed{D.\ -12}$