If the function y= x^3 + ax^2 + 3x -1 is always increasing, find the range of possible values of a.
First, i differentiated it. 3x^2 +2ax +3 . This is a quadratic expression. Now, for the equation to be positive b^2 > 4ac . 4a^2 > 4 x 3 x 3 . a^2 > 9 so a >3 and a <-3 . But the answer sheet says -3
Please, what did i do wrong? Please show explanation, working/ method. Thank you
I will award 10 points to best answer
First, i differentiated it. 3x^2 +2ax +3 . This is a quadratic expression. Now, for the equation to be positive b^2 > 4ac . 4a^2 > 4 x 3 x 3 . a^2 > 9 so a >3 and a <-3 . But the answer sheet says -3
Please, what did i do wrong? Please show explanation, working/ method. Thank you
I will award 10 points to best answer
-
Hello.
You should notice some immediate red flags with your answer, because if you plug in -4 for a, b^2 > 4ac is not true. Same if you plug in positive 4.
I don't know how to work it, though. Sorry.
You should notice some immediate red flags with your answer, because if you plug in -4 for a, b^2 > 4ac is not true. Same if you plug in positive 4.
I don't know how to work it, though. Sorry.