How do you solve $x^2 - 4x = 5$ by completing the square?

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Answer 1 · 2015-05-15T17:23:45

$x^2 - 4x = 5$
To write the Left Hand Side as a Perfect Square, we add 4 to both sides:

$x^2 - 4x + 4 = 5 + 4$

$x^2 -2.2.x + 2^2 = 9$
$x^2 -2.2.x + 2^2 = 3^2$

Using the Identity $color(blue)((a-b)^2 = a^2 -2ab + b^2$ , we get
$(x - 2)^2 = 9$

$x - 2 = sqrt9$ or $x - 2 = -sqrt9$

$color(green)(x = sqrt 9 +2$ or $color(green)(x = -sqrt 9 + 2$

How do you solve x^2 - 4x = 5x^2 - 4x = 5 by completing the square?