Loading [MathJax]/jax/element/mml/optable/Latin1Supplement.js

User interface language: English | Español

Date November 2019 Marks available 6 Reference code 19N.2.AHL.TZ0.H_6
Level Additional Higher Level Paper Paper 2 Time zone Time zone 0
Command term Find Question number H_6 Adapted from N/A

Question

Let P(z)=az337z2+66z10, where zC and aZ.

One of the roots of P(z)=0 is 3+i. Find the value of a.

Markscheme

METHOD 1

one other root is 3i         A1

let third root be α       (M1)

considering sum or product of roots       (M1)

sum of roots =6+α=37a         A1

product of roots =10α=10a         A1

hence a=6         A1

 

METHOD 2

one other root is 3i         A1

quadratic factor will be z26z+10       (M1)A1

P(z)=az337z2+66z10=(z26z+10)(az1)       M1

comparing coefficients       (M1)

hence a=6         A1

 

METHOD 3

substitute 3+i into P(z)       (M1)

a(18+26i)37(8+6i)+66(3+i)10=0       (M1)A1

equating real or imaginary parts or dividing       M1

18a296+19810=0  or  26a222+66=0  or  1066(3+i)+37(8+6i)18+26i         A1

hence a=6         A1

 

[6 marks]

Examiners report

[N/A]

Syllabus sections

Topic 1—Number and algebra » AHL 1.14—Complex roots of polynomials, conjugate roots, De Moivre’s, powers & roots of complex numbers
Show 55 related questions
Topic 1—Number and algebra

View options