Question

Identify the x-coordinates for the interval where y = x^3 + 3x^2 - 2x + 4 is decreasing.

Answer 1

y = x^3 + 3x^2 - 2x + 4
y' = ...?
wherever y' = -ve, the gradient is downhill, so y is decreasing
so work out turning points to indicate change in gradient from neg to positive

Answer 2

Answer is written in the form (left x, right x).
-∞ means the left x-coordinate continues to decrease without end
∞ means to right x-coordinate continues to increase without end
Select one:
a. (0.3, ∞)
b. (-∞, -2.3)
c. (-2.3, 0.3)
d. (-∞, ∞)