Question 11
- Using a scale of 2 cm to 1 unit on the x – axis and 2 cm to 2 units on the y – axis, draw the
graph for 𝑦=𝑥2+12. -
-
Use the graph to:
- solve 𝑥2 = 5
- find the range of values of x for which y decreases as x increases.
| X | −4 | −43 | −2 | −1 | 0 | 1 | 2 | 3 | 4 |
| Y | 9.5 | 0.5 |
Observation
The Chief Examiner reported that performance on this question was not quite encouraging as
majority of the candidates’ were able to complete the table and drew the graph but did not answe
the question that followed
In part (a), they completed the table as expected
| X | −4 | −3 | −2 | −1 | 0 | 1 | 2 | 3 | 4 |
| Y | 16.5 | 9.5 | 4.5 | 1.5 | 0.5 | 1.5 | 4.5 | 9.5 | 16.5 |
In part (b), using the completed table, they did as expected by drawing the graph of y as shown:
In part (c) (i), they were required to solve for x2 = 5. But y = x2 + 12 and when we substitute for x2 ,
y = 5.5. Next, they were to draw the line y = 5.5. The point of intersections of the two graphs is the
solution to x2 = 5, which is x = -2.3 ± 0.1 and 2.3 ± 0.1.
In part (c) (ii), reading from the graph, the range of values of x for which y decreases is −4≤𝑥0.