JAMB Mathematics 2009 Objective — Question 14

Question 14 of 50 from the Joint Admissions and Matriculation Board (JAMB) Mathematics 2009 Objective paper, with the correct answer and a full explanation.

Which of the following equations represents the graph above (a parabola crossing x-axis near -2 and 1/4, with y-intercept at 2)?

A. y=2+7x+4x^2
B. y=2-7x+4x^2
C. y=2+7x-4x^2Correct
D. y=2-7x-4x^2

Explanation

The graph cuts the x-axis at x=-2, also the graph is a quadratic graph that is concave down (n-shape), i.e. a<0. At y=0, x=-2 and x=1/4: (x+2)(4x-1)=0 gives 4x^2+7x-2=0, i.e. multiply by -1: -4x^2-7x+2=0, rearranged as y=2+7x-4x^2.

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