Homework Help: Math- Algebra II

Posted by Christina on Wednesday, January 5, 2011 at 10:07pm.

x^2-4x+12=0 Complete the square to solve for x.

Okay I know how to do up to here:

(-4/2)^2 -12=x^2-4x(-4/2)^2

2-12= x^2-4x+2
-10= DO I FACTOR IT?

Math- Algebra II - Reiny, Wednesday, January 5, 2011 at 10:46pm
x^2 - 4x = -12
x^2 - 4x + 4 = -12 + 4
(x-2)^2 = -8
x-2 = ą √-8 , but √-8 = 2√2 √-1 = 2i√2

x = 2 ą 2i√2
Math- Algebra II - Kay, Wednesday, January 5, 2011 at 11:08pm
Easist way always is to go and get the roots:

(-b + sqrt(b^2 - 4ac)) / 2a
-
x^2 -4x +12 = 0

a= 1, b=-4 c = 12

(-(-4) + sqrt(16 - 4*12)) / 2
-

(4 + sqrt(-32))/2
-

4 + sqrt(i^2 * 16 *2))/2
-

note : i^2 = -1

(4 + i 4 sqrt(2))/2
-

Ans:

2+ 2i sqrt(2)
-

are the two roots

Hope this helps Christine!

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