Determine all x such that the function f(x)=−x3+2x2+7x+12 is increasing.
Antwoord 1 correct
Correct
Antwoord 2 optie
All x
Antwoord 2 correct
Fout
Antwoord 3 optie
−213≤x≤1
Antwoord 3 correct
Fout
Antwoord 4 optie
The correct answer is not among the other options.
Antwoord 4 correct
Fout
Antwoord 1 optie
−1≤x≤213.
Antwoord 1 feedback
Correct: f′(x)=−3x2+4x+7.
Zeros: x1=−4−√42−4⋅−3⋅72⋅−3=213 and x2=−4+√42−4⋅−3⋅72⋅−3=−1.
Via a sign chart of f′(x) (for instance with f′(−2)=−13, f′(0)=7 and f′(3)=−8) we find that f′(x)≥0 for −1≤x≤213.
Go on.
Zeros: x1=−4−√42−4⋅−3⋅72⋅−3=213 and x2=−4+√42−4⋅−3⋅72⋅−3=−1.
Via a sign chart of f′(x) (for instance with f′(−2)=−13, f′(0)=7 and f′(3)=−8) we find that f′(x)≥0 for −1≤x≤213.
Go on.
Antwoord 2 feedback
Antwoord 3 feedback
Wrong: Note that you have to use −b in calculating the zeros of a quadratic equation.
See Extra explanation: zeros.
See Extra explanation: zeros.
Antwoord 4 feedback
Wrong: The correct answer is among them.
Try again.
Try again.