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Date November 2010 Marks available 2 Reference code 10N.1.sl.TZ0.13
Level SL only Paper 1 Time zone TZ0
Command term Write down Question number 13 Adapted from N/A

Question

Consider the function \(f(x) = p{(0.5)^x} + q\) where p and q are constants. The graph of f (x) passes through the points \((0,\,6)\) and \((1,\,4)\) and is shown below.

Write down two equations relating p and q.

[2]
a.

Find the value of p and of q.

[2]
b.

Write down the equation of the horizontal asymptote to the graph of f (x).

[2]
c.

Markscheme

p + q = 6     (A1)

0.5p + q = 4     (A1)     (C2)


Note: Accept correct equivalent forms of the equations.

 

[2 marks]

a.

p = 4, q = 2     (A1)(A1)(ft)     (C2)


Notes: If both answers are incorrect, award (M1) for attempt at solving simultaneous equations.

 

[2 marks]

b.

y = 2     (A1)(A1)(ft)     (C2)


Notes: Award (A1) for “y = a constant”, (A1)(ft) for 2. Follow through from their value for q as long as their constant is greater than 2 and less than 6.

An equation must be seen for any marks to be awarded.

 

[2 marks]

c.

Examiners report

A significant number of candidates found it difficult to identify and write two equations that relate p and q. Many of those who wrote the equations were unable to solve them or use their GDC to find the values of p and q in part b). Although the question in part c) was quite standard, there were many errors in the responses. Many students wrote x = 2 or only 2 instead of y = 2.

a.

A significant number of candidates found it difficult to identify and write two equations that relate p and q. Many of those who wrote the equations were unable to solve them or use their GDC to find the values of p and q in part b). Although the question in part c) was quite standard, there were many errors in the responses. Many students wrote x = 2 or only 2 instead of y = 2.

b.

A significant number of candidates found it difficult to identify and write two equations that relate p and q. Many of those who wrote the equations were unable to solve them or use their GDC to find the values of p and q in part b). Although the question in part c) was quite standard, there were many errors in the responses. Many students wrote x = 2 or only 2 instead of y = 2.

c.

Syllabus sections

Topic 6 - Mathematical models » 6.4 » Concept and equation of a horizontal asymptote.

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