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quadratic formula FAIL or is it just me?

ok so like everyone knows that the roots for x^2+7x+6 is x= -1, -6
yet the quadratic formula -b+or-squaroot b^2-4ac
2a
tells me the roots are -19/2 and -9/2
its second time i come across a questiona where the quadratic formula gives me different roots to factorising. where hav i gone wrong?
Original post by alevelshmaylevel92
ok so like everyone knows that the roots for x^2+7x+6 is x= -1, -6
yet the quadratic formula -b+or-squaroot b^2-4ac
2a
tells me the roots are -19/2 and -9/2
its second time i come across a questiona where the quadratic formula gives me different roots to factorising. where hav i gone wrong?


where is your working?
Reply 2
Avatar for Ben121
Ben121
4
(-7 +- sqrt(25)) / 2
It's ALL over 2a, not just the square root bit.
Reply 4
Avatar for Ollie901
Ollie901
1
Original post by alevelshmaylevel92
ok so like everyone knows that the roots for x^2+7x+6 is x= -1, -6
yet the quadratic formula -b+or-squaroot b^2-4ac
2a
tells me the roots are -19/2 and -9/2
its second time i come across a questiona where the quadratic formula gives me different roots to factorising. where hav i gone wrong?


(-7 +- root(49- 4x1x6))/2

=

(-7 +- root25)/2

=

(-7 +- 5)/2

=

-1, -6
Reply 5
Avatar for 1.2.3.
1.2.3.
Lol, I think it is just you.
...Yeah

it's you.
Original post by alevelshmaylevel92
ok so like everyone knows that the roots for x^2+7x+6 is x= -1, -6
yet the quadratic formula -b+or-squaroot b^2-4ac
2a
tells me the roots are -19/2 and -9/2
its second time i come across a questiona where the quadratic formula gives me different roots to factorising. where hav i gone wrong?


x=(-(7)+/- sqrt(49-4*6))/2


=(-7 +/- sqrt 25)/2


x= (-7 - 5)/2 = (-12)/2 = -6 OR (-7+5)/2 = (-2)/2 = -1

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