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2005 P2 Q11 - HSN forum

# 2005 P2 Q11

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### #1Hev

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Posted 18 May 2006 - 03:36 PM

11 b.

[x=-1 in the solution of the cubic equation x^3 + px^2 +px +1 = 0]

Hence find the range of values for p for which all the roots of the cubic equations are real. (7 marks)

Can anyone help me please? I'm beyond useless at these questions!

This year's Fenella Feline (CAT) in Peterhead's Pantomine Pinocchio!

### #2George

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Posted 18 May 2006 - 03:45 PM

OK, since x= -1 is a root, you can factorise to get .

The roots of that equation will all be real if the roots of are both real.

Now, you can have a look at the examples in the Polynomials and Quadratics notes - sections 2 and 6 should be helpful

### #3Hev

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Posted 18 May 2006 - 03:50 PM

Thanks, i just didn't even know where to start!

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### #4will_789

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Posted 18 May 2006 - 03:58 PM

Now use the discriminant
b -4ac 0

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