How do you find the roots, real and imaginary, of y=2(x+3)^2-(x-3)^2 using the quadratic formula?

1 Answer
Dec 29, 2015

y=2(x+3)^2-(x-3)^2
implies y=2(x^2+6x+9)-(x^2-6x+9)
implies y=2x^2+12x+18-x^2+6x-9
implies y=x^2+18x+9
For finding roots becomes #0. implies x^2+18x+9=0#

The quadratic formula is
If ax^2+bx+c=0 then x=(-b+-sqrt(b^2-4ac))/(2a)
Here a=1 b=18 and c=9

implies x=(-18+-sqrt(18^2-4*1*9))/(2*1)

implies x=(-18+-sqrt(324-36))/(2)

implies x=(-18+-sqrt(324-36))/(2)

implies x=(-18+-sqrt(288))/(2)

implies x=(-18+-sqrt(288))/(2)

implies x=(-18+-12sqrt(2))/(2)

implies x=(2(-9+-6sqrt(2)))/(2)

implies x=(-9+-6sqrt(2))