Find the set of values for which: x^2 - 3x - 18 > 0
Factorise the equation to find the critical values:
x^2 - 3x - 18 > 0 (x-6)(x+3) > 0
Critical values:x - 6 = 0x = 6
x + 3 = 0x = -3
Draw a graph where a parabola (shape of a quadratic equation) intersects the x axis at x=6 and x=-3From this, can see that the graph takes values bigger than 0 in the ranges of x>6 and x<-3
Answer:x > 6x < -3
Can check answer by plugging in values for x from this range into the equation, e.g. x = 7, f(x) = 10 which is bigger than 0. x = -4, f(x) = 10 which is bigger than 0.
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