How do you solve 2x^2 - 4x -1=0 by completing the square?

1 Answer
Nov 19, 2016

x = 2.22 " or " x = 0225

Explanation:

2x^2 -4x -1 =0

Divide both sides by 2 to get just x^2

x^2 -2x-1/2 =0" "larr move -1/2 to the other side
x^2 -2x " "= 1/2" "larr add color(red)((-2/2)^2) to both sides
x^2 -2x " "color(red)(+1)= 1/2 color(red)(+1)

(x-1)^2" "=3/2" "larr write as square of a binomial

x-1" "=+-sqrt(3/2)" "larr find square root of each side

x = +sqrt(3/2)+1" "or x = -sqrt(3/2)+1" "larr solve for x

x = 2.22 " or " x = 0225