How do you solve using the completing the square method 2x2+8x+1=0?

2 Answers
P dilip_k
Feb 27, 2016

2x2+8x+1=0
Dividing both sides by 2 we get
⇒x2+4x+12=0
⇒x2+2⋅x⋅2+22−22+12=0
⇒x2+2⋅x⋅2+22=4−12=72
⇒(x+2)2=72
⇒x+2=±√72
⇒x=−2±√72

Noah G
Feb 27, 2016

See solution below.

Explanation:

2(x2+4x+m)=−1

m=(b2)2

m=(42)2

m=4

2(x2+4x+4−4)=−1

2(x+2)2−4(2)=−1

2(x+2)2=−1+8

(x+2)2=72

x+2=±√72

x=±√72−2

Don't forget the ± sign with the square root. Remember: a quadratic equation must always have two solutions.

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