General Mathematics Paper 2,May/June. 2012
 Questions: 1 2 3 4 5 6 7 8 9 10 11 12 13 Main
Weakness/Remedies
Strength

Question 12

Copy and complete the table of values for y = 1 – 4 cos x.

 X 0° 30° 60° 90° 120° 150° 180° 210° 240° 270° 300° Y -3.0 1.0 4.5 -1.0

(b)     Using a scale of 2cm to 30o on the x-axis and 2 cm to 1 unit on the y – axis, draw the graph of y = 1 – 4 cos x for 0o ≤ x ≤ 300o.

(c)      Use the graph to:
(i)      solve the equation 1 – 4cosx = 0;

1. find the value of y when x = 105;
2. find x when y = 1.5.

_____________________________________________________________________________________________________
Observation

The report stated that this question was not attempted by majority of the candidates and only a few of those who attempted the question were able to complete the table of values correctly.  Majority of those who were able to draw the graph could not read correctly from the graph.  Candidates were expected to complete the table as follows:

Candidates would then use this table and the scale provided to draw the graph of the relation y = 1-4cos x and use this graph to answer the questions that followed.

From the graph, the solution of 1-4cos x = 0 was 75o and 285o while y was 1.9 when x was 105.  The values of x when y = 1.5 were obtained by drawing the line y = 1.5 to meet the curve y = 1-4cos x.  The required solutions were the values of x at the points of intersection of the two graphs which were 97o and 264o ± 3.