A classic geometry question and a good one too.
Let's solve this
First of all, we know that the graph represented by the equation (E) \(y = -x^2 + 9\) intersects line L in two points : A (p,5) and B (t, -7).
This automatically tells us that points A and B satisfy equation (E).As such, we'll have the following two equations :
(1) : \(5 = - p^2 + 9\) which yields \(p^2 = 4\) meaning that \(p = 2\) or \(p = -2\)
(2) : \(- 7 = -t^2 + 9\) which yields \(t^2 = 16\) meaning that \(t = 4\) or \(t = -4\)
(Remember that even powers hide the sign of the base so always include the negative answers unless told otherwise by the question stem)Considering the answers we've obtained, we have 4 possibilities for points A and B :
Possibility n°1 : A (2,5) and B (4,-7)
Possibility n°2 : A (2,5) and B (-4, -7)
Possibility n°3 : A (-2,5) and B (4, -7)
Possibility n°4 : A (-2,5) and B (-4,-7)
As a reminder :
1/ In a xy-coordinate plane, a line is defined by the following equation : \(y = a*x + b\) (with
a being the slope of the line)
2/ Given two points \(A (x1,y1)\) and \(B (x2,y2)\), the slope of a line can be computed as such :\(a = \frac{(y2-y1)}{(x2-x1)}\)
So considering reminder n°2, for each of the possibilities above we get as a value for the slope of line L :
Possibility n°1 : a = -6
Possibility n°2 : a = 2
Possibility n°3 : a = -2
Possibility n°4 : a = 6
As such the least possible value of the slope of line L is -6, which is answer choice D.Hope that helped