How do you solve using the completing the square method 2x^2+8x-10=0?

2 Answers
Monzur R.
Feb 3, 2017

x=-5
x=1

Explanation:

2x^2+8x-10=2[x^2+4x-5]

2[x^2+4x-5]=2[(x+2)^2-2^2-5]=2[(x+2)^2-9]=

2(x+2)^2-18=0

2(x+2)^2=18

(x+2)^2=9

x+2=+-3

x=+-3-2

x=-5

x=1

Andy Y.
Feb 3, 2017

x=1 or x=-5

Explanation:

Divide both sides by 2 to get rid of the coefficient of x^2

x^2+4x-5=0

Add 5 to both sides

x^2+4x=5

Take half the coefficient of x, square it, and add to both sides

  • The coefficient of x is 4
  • Half that is 2
  • The square of 2 is 4
  • Adding 4 to both sides gives

x^2+4x+4=9

Factoring the left hand side gives

(x+2)^2=9

The square root of both sides gives

x+2=3 or x+2=-3
x=1 or x=-5

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