WAEC Mathematics 2011 Paper

Concept:Use the given graph of $y = x^{2} - 3x - 3$ to solve the equation by rewriting it as a horizontal line intersection.Explanation:We need values of $x$ such that $x^{2} - 3x = 7$. Rewrite as $x^{2} - 3x - 7 = 0$. The graph shows $y = x^{2} - 3x - 3$. Add $4$ to both sides of the equation: $x^{2} - 3x - 7 + 4 = 4$. This gives $x^{2} - 3x - 3 = 4$. So the required $x$-values occur where $y = 4$ on the graph. Draw the horizontal line $y = 4$ on the graph. It cuts the curve at $x \approx -1.55$ and $x \approx 4.55$.Answer:D. $1.55, 4.55$