00:01
Hi, in this question given that f of x equals 2x cube minus 3x square minus 12x plus 8.
00:14
In part a, we have to find all the points on the graph of f of x which tangent line is horizontal.
00:21
We know that the condition tangent line is horizontal when dy by dx equals 0.
00:34
So this is y.
00:37
First we have to find dy by dx.
00:40
On differentiating the given function then we get 6x square minus 6x minus 12.
00:49
Next we have to equate with 0 so that we get 6x square minus 6x minus 12 equals 0.
00:56
On dividing by 6 then we get x square minus x minus 2 equals 0.
01:02
Next we have to find the roots minus 2 minus 1.
01:06
So we have to choose the roots as minus 2 and plus 1.
01:11
So x minus 2 into x plus 1 equals 0.
01:16
Therefore x equals 2 and x equals minus 1.
01:20
Next we have to evaluate f of 2 which is equal to 2 into 2 the whole cube minus 3 into 2 the whole square minus 12 into 2 plus 8...