Question

7. Given that y=px²−5x+q, and the table gives values of x and y. (a)(i) Use the table to find the values of p and q. (ii) Copy and complete the table. (b) Using scales of 2cm to 1 unit on the x-axis and 2cm to 5 units on the y-axis, draw the graph of the relation for −3≤x≤5. (c) Use the graph to find: (i) y when x=1.8; (ii) x when y=−8.

Accepted Answer

(a)(i) Using the points (0,−12) and (4,0) from the table: at x=0, y=q=−12. At x=4: 0=p(16)−5(4)+(−12) → 0=16p−20−12 → 16p=32 → p=2.
So the relation is y=2x²−5x−12.
(a)(ii) Completing the table using y=2x²−5x−12 for each given x-value.
(c)(i) Reading from the graph, when x=1.8, y ≈ −14.5.
(c)(ii) Reading from the graph, when y=−8, x ≈ −0.6 or x ≈ 3.1.

WAEC Mathematics 2015 Theory — Question 12

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