Question

Solve x 2 - 4x - 7 = 0 by completing the square. What are the solutions?

a) {2 + squrt of 11, 2 -squrt of 11}
b) {-2 + squrt of 11, -2 - squrt of 11}
c) {2 +squrt of 7, 2 +squrt of 7}

Answer 1

http://www.mathwarehouse.com/quadratic/quadratic-formula-calculator.php

Answer 2

http://www.youtube.com/watch?v=gzm-uhj06q8 migth help

it comes from expanding
(x+a)^2 which is a perfect square
(x+a)(x+a)=
x^2+2ax+a^2 is a perfect square
A B C
x 2 - 4x - 7 = 0 is not PS so we must put it in such a form

Answer 3

Okay thank you the video helped @timo86m

Answer 4

the process is called completing the square
x 2 - 4x - 7 = 0

always get the constant term on the right which is -7 so we add 7

x 2-4x=7

That move enables us to add a constant term to the left which will make it a comple perfect square.
----
we already estaplished that
x^2+2ax+a^2 is a perfect square
A B C

We got
x 2 -4x +? we need to find that constant term
A B C

we know it is a^2 and we know

B=-4
B=2a

if we plug in
-4=2a then solve for a
-4/2=a = -2

we add it to both sides since it is algebra and whatever you do to one side you do to the other

x 2 -4x+(-2^2)=7+(-2^2)
x 2 -4x+4=7+4
x 2 -4x+4=11

since x 2 -4x+4 is a perfect square represent by (x+a)^2 then

(x-2)^2=11

x-2= +-sqrt(11) +- is plus or minus

x=+-sqrt(11) +2

x=+-3.3166 +2

so x can be 5.31... or -1.31...

Answer 5

A