00:01
Suppose h of t equals 3 halves times t raised to the 4th power minus t to the 6th.
00:06
For the first part, we want to find the open intervals in which the function is increasing and decreasing.
00:12
So to do this, we first want to get h prime of t, and this is just 3 halves times 4t raised to the 3rd power minus 6t raised to the 5th power.
00:24
That's equal to 6 t raised to the third power minus 6 t raised to the fifth power.
00:32
And then we want to set h prime of t equal to zero, solve for t, to get the critical numbers of the function.
00:40
That means you have 6 t raised to the third power minus 6 t raised to the fifth power equal to zero.
00:45
We factor out 6t raise to the third power.
00:48
That's going to give us 1 minus t squared equal to 0.
00:53
That means t is zero or t equals plus or minus one and then you want to partition our domain which in this case is all real numbers from negative infinity to infinity using the critical numbers zero negative one and one so let's say this is our number line then you'll partition this you have negative one zero and then one so the possible interval will be from negative infinity to negative 1, negative 1 to 0, 0 to 1, and then 1 to infinity.
01:32
And then you want to do first derivative test to get the sign and the conclusion for the behavior of the function.
01:42
And then to get the sign, we need the test values for each interval.
01:47
So let's say we use negative 2 here, negative 0 .5, positive 0 .5, and then 2.
01:55
2 here.
01:56
When t is equal to negative 2, if we are to use the factored form of h prime, which is this, this 6t raise of the third power is going to be negative, and 1 minus t squared is also negative, so that makes a positive h prime.
02:14
If it's negative 0 .5, 6t cube is still negative, but 1 minus t squared becomes positive, so h prime is now negative.
02:24
If it's positive, 0 .5 ,000, 0 .5, the cubic factor is positive, but 1 minus t squared is still positive...