JAMB Mathematics 2011 Paper

Concept:Solve the quadratic inequality by moving all terms to one side and finding the sign intervals of the factorised expression.Explanation:Rewrite the inequality:$x^2 + 2x > 15$$x^2 + 2x - 15 > 0$Factorise the quadratic:$x^2 + 2x - 15 = (x + 5)(x - 3)$So, $(x + 5)(x - 3) > 0$.The critical points are $x = -5$ and $x = 3$.Test the sign of $(x + 5)(x - 3)$ on the intervals:For $x < -5$, both factors are negative, so the product is positive.For $-5 < x < 3$, the product is negative.For $x > 3$, both factors are positive, so the product is positive.Therefore, the inequality holds when $x < -5$ or $x > 3$.This means $x > 3$ or $x < -5$.Answer:$x > 3$ or $x < -5$.Option D.