Roots of Polynomials (Edexcel A Level Further Maths: Core Pure)

Exam Questions

35 mins4 questions
1
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9 marks

straight f left parenthesis straight z right parenthesis equals straight z to the power of 4 plus az cubed plus 6 straight z squared plus bz plus 65

where a and b are real constants.

Given that z equals 3 plus 2 straight i is a root of the equation straight f left parenthesis straight z right parenthesis = 0, show the roots of straight f left parenthesis straight z right parenthesis equals 0  on a single Argand diagram.

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2
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8 marks

The roots of the equation

x cubed minus 8 x squared plus 28 x minus 32 equals 0

are alpha comma space beta and gamma

Without solving the equation, find the value of

(i)   1 over alpha plus 1 over beta plus 1 over gamma

(ii)   left parenthesis alpha plus 2 right parenthesis left parenthesis beta plus 2 right parenthesis left parenthesis gamma plus 2 right parenthesis

(iii)   alpha squared plus beta squared plus gamma squared

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3a
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7 marks

straight f left parenthesis straight z right parenthesis equals 3 straight z cubed plus pz squared plus 57 straight z plus straight q

wherespace p and q are real constants.

Given that 3 minus 2 square root of 2 straight i is a root of the equation straight f left parenthesis straight z right parenthesis equals 0

(a)
show all the roots of straight f left parenthesis straight z right parenthesis equals 0 on a single Argand diagram,
3b
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3 marks
(b)
find the value ofspace p and the value of q.

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4
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8 marks

The roots of the equation

x cubed minus 2 x squared plus 4 x minus 5 equals 0

are p comma space q and r.
Without solving the equation, find the value of

(i)   2 over p plus 2 over q plus 2 over r

(ii)   left parenthesis space p space – space 4 right parenthesis left parenthesis q space – space 4 right parenthesis left parenthesis r space – space 4 right parenthesis

(iii)   p cubed space plus space q cubed space plus space r cubed

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