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Solve the quadratic equation by completing the square.  3x^2 + 12x + 39 = 0

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kristenmarieb... | Student, Grade 10 | Valedictorian

Posted May 14, 2013 at 3:36 AM via web

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Solve the quadratic equation by completing the square. 

3x^2 + 12x + 39 = 0

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pramodpandey | College Teacher | Valedictorian

Posted May 14, 2013 at 3:58 AM (Answer #1)

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We have given

`3x^2+12x+39=0`

factor out 3 because HCF(3,12,39)=3

`x^2+4x+13=0`

 We wish to write it as

`A^2+2AB+B^2=(A+B)^2`

Thus

x^2+4x+4+9=0

(x+2)^2=-9

(x+2)^2= 9i^2

Taking square root ,both side ,we have

x+2=+-sqrt(9i^2)

x=-2+-3i

Thus

x=-2-3i

x=-2+3i

 

 

 

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