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Date May Example question Marks available 1 Reference code EXM.3.AHL.TZ0.5
Level Additional Higher Level Paper Paper 3 Time zone Time zone 0
Command term Show that Question number 5 Adapted from N/A

Question

This question will diagonalize a matrix and apply this to the transformation of a curve.

Let the matrix M=(52121252).

Let (12121212)=R1.

Let R(xy)=(XY).

Let (130012)(XY)=(uv).

Hence state the geometrical shape represented by

Find the eigenvalues for M. For each eigenvalue find the set of associated eigenvectors.

[8]
a.

Show that the matrix equation (xy)M(xy)=(6) is equivalent to the Cartesian equation 52x2+xy+52y2=6.

[2]
b.

Show that (1212) and (1212) are unit eigenvectors and that they correspond to different eigenvalues.

[2]
c.i.

Hence, show that M(12121212)=(12121212)(2003).

[1]
c.ii.

Find matrix R.

[2]
d.i.

Show that M=R1(2003)R.

[1]
d.ii.

Verify that (XY)=(xy)R1.

[3]
e.i.

Hence, find the Cartesian equation satisfied by X and Y.

[2]
e.ii.

Find the Cartesian equation satisfied by u and v and state the geometric shape that this curve represents.

[2]
f.

State geometrically what transformation the matrix R represents.

[2]
g.

the curve in X and Y in part (e) (ii), giving a reason.

[2]
h.i.

the curve in x and y in part (b).

[1]
h.ii.

Write down the equations of two lines of symmetry for the curve in x and y in part (b).

[2]
i.

Markscheme

|52λ121252λ|=0(52λ)2(12)2=052λ=±12λ=2or3       M1M1A1A1

λ=2     (12121212)(pq)=(00)q=p      eigenvalues are of the form t(11)       M1A1

λ=3     (12121212)(pq)=(00)q=p     eigenvalues are of the form t(11)       M1A1

[8 marks]

a.

(xy)(52121252)(xy)=(6)(52x+12y12x+52y)(xy)=(6)      M1A1

(52x2+12xy+12xy+52y2)=(6)52x2+xy+52y2=6.       AG

[2 marks]

b.

(1212)=12(11) corresponding to λ=2,     (1212)=12(11) corresponding to λ=3      R1R1

[2 marks]

c.i.

M(1212)=2(1212)andM(1212)=3(1212)M(12121212)=(12121212)(2003)      A1AG

[1 mark]

c.ii.

Determinant is 1.   R=(12121212)        M1A1

[2 marks]

d.i.

MR1=R1(2003) so post multiplying by R gives M=R1(2003)R       M1AG

[1 mark]

d.ii.

(12121212)(xy)=(XY)(12x12y12x+12y)=(XY)(XY)=(12x12y12x+12y)         M1A1

and (xy)(12121212)=(12x12y12x+12y) completing the proof       A1AG

[3 marks]

e.i.

(xy)M(xy)=(6)(xy)R1(2003)R(xy)=(6)(XY)(2003)(XY)=(6)

(2X2+3Y2)=(6)X23+Y22=1       M1A1

[2 marks]

e.ii.

X3=u,Y2=vu2+v2=1, a circle (centre at the origin radius of 1)     A1A1

[2 marks]

f.

A rotation about the origin through an angle of 45° anticlockwise.    A1A1

[2 marks]

g.

an ellipse, since the matrix represents a vertical and a horizontal stretch    R1A1

[2 marks]

h.i.

an ellipse      A1

[1 mark]

h.ii.

y=xy=x      A1A1

[2 marks]

i.

Examiners report

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b.
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c.i.
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c.ii.
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d.i.
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d.ii.
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e.i.
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e.ii.
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g.
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h.i.
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h.ii.
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i.

Syllabus sections

Topic 1—Number and algebra » AHL 1.15—Eigenvalues and eigenvectors
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Topic 1—Number and algebra

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