Apps. and Interpretation for IBDP Maths Ebook 1 | Page 30

Your Practice Set – Applications and Interpretation for IBDP Mathematics
6
Paper 1 – -intercepts and Coordinates of Vertex
Example
Let
2
f ( x) � 3x �12x
� 15 . Part of the graph of f is shown below.
(a)
Find the x -intercepts of the graph.
(b) (i) Write down the equation of the axis of symmetry.
[4]
(ii)
Find the y -coordinate of the vertex.
[3]
Solution
(a) f( x) � 0
(M1) for function equals to 0
2
3x
�12x�15 � 0
3( x�1)( x�5) � 0
A1
x �� 1 or x � 5
Thus, the x -intercepts are � 1 and 5. A2 N4
(b) (i) x � 2
A1 N1
[4]
(ii)
The y -coordinate of the vertex
2
� 3(2) �12(2) � 15
(M1) for substitution
�� 27
A1 N2
[3]
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