SPM 2020 Add Maths Paper 1, Question 6Quadratic Functions

Solved on video in English and Bahasa Melayu · 4 marks · Form 4, Quadratic Functions · 3:50 video

The question

(a)

It is given the graph of the quadratic function f(x) = -(2x + 3h)² + k - 4, where h and k are constants, touches the x-axis at one point. State the value of k.

[2 marks]

(b)

State the equation of the axis of symmetry of the curve in terms of h.

[2 marks]

SPM 2020 Add Maths Paper 1, Question 6: the question as drawn in Eduly's video3:50

Part (a)

Step 1

The function is in vertex form; its maximum value is k - 4, attained when (2x + 3h)² = 0.

Why this step

The square is never negative and the minus flips the curve, so the top is k − 4. Reading this off beats expanding for b² − 4ac.

2 more steps, each with the reason for it, in the full solution

Final answer

k = 4

Where students lose marks

Watch out: don't expand the square and use b² − 4ac = 0. Read the vertex form: the maximum value k − 4 must equal 0.

Part (b)

4 more steps, each with the reason for it, in the full solution

Final answer

x = −3h/2

Where students lose marks

Watch out: write the answer as an equation, x = −3h/2. Just '−3h/2' is an expression, not the equation of the axis.

Watch every step of this question solved on video (3:50), with the reason behind each step and a box that checks your own answer.

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