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math

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completing the square
3x^2 +15 -33 =0
a=3
b=15
c=-33

-15+or- sqrt225-4*3*-33/2*3

-15+or-sqrt225+396/6

is this right because don't you have to subtract not add the 396

please help. thanks

  • math -

    3x²+15x-33
    a=3, so
    =3(x²+5x-11)
    =3[(x+2.5)²-11-2.5²]
    =3[(x+2.5)²-(√(17.25))²]
    =3(x+2.5+√(17.25))(x+2.5-√(17.25)))
    So
    x=-2.5±√(17.25)
    which you can also express integers as follows:
    x=[-5±√(69)]/2

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