00:02
In this problem, we want to sketch the graph of a function f with the stated properties.
00:06
And then i want to discuss the signs of f ' and f ''.
00:10
So a, the function f is concave up and increasing over the interval minus infinity and plus infinity.
00:20
So first let's discuss what does it mean for a function to be concave up.
00:34
So a function f is concave up if its second derivative is positive and the function f of x will have a positive concavity.
00:57
On the other hand, a function is concave down if its second derivative is negative and in this case the function f of x has a negative concavity like so.
01:17
And so we notice that when a function is concave up, on the left hand side here we have a decreasing function and on the right we have an increasing function.
01:30
So in our first question, when the function f is concave up and increasing, then we only have this upward slope.
01:42
So a function like an exponential would be a good candidate.
02:00
So here we have an example where f ' of x is positive because it is always increasing and f ' of x is also always positive because it is concave up.
02:18
B, we want to draw a function f that is concave down yet increasing from minus infinity to plus infinity.
02:26
So looking at this concave down shape, we are only interested in this right hand portion where the function is always increasing...