00:01
Hello, we have to solve the following problem.
00:02
First, in part a, we have to write down the differential equation.
00:06
Here, emf minus inductance times di over dt minus ir equals to zero.
00:14
What does it mean? it means that, first of all, let's write that i is small.
00:21
So it means that here emf is i as a function of time times resistance plus l times di over dt.
00:30
And now we have to substitute parameters with numbers.
00:34
So let's do this.
00:36
It means that here 2di over dt plus 300i as a function of time equals to 15 cosine of 300t.
00:56
So we've answered equation a.
00:59
Now, in equation b, we have to solve this equation.
01:02
And we need to make the substitution, which is i as a function of time equals to a cosine 300t plus b sine 300t.
01:18
How does it help us? now let's find di over dt.
01:25
And now let's rewrite this equation.
02:23
And now we have to simplify this expression.
02:28
Let's do this.
02:32
Actually, let me double check it.
02:47
Let's check the coefficients.
02:51
So let's see what coefficients we have here...