00:01
Understand the definition of a linear differential equation.
00:08
Okay, so a linear differential equation is an equation that involves an unknown function and its derivatives.
00:14
It is linear if it can be written in the form a n of t d n y by d t to the n plus all the way down to a 1 of t d y by d t plus a naught ty equals g of t.
00:41
So looking at the options given here, if we see terms like y squared or sine y or any other nonlinear combination of functions, then the equation is sort of nonlinear, if that makes sense.
01:03
So we want these constants a1 of t, a0 of t, an of t to be functions in terms of t, not in terms of y.
01:17
So let's look at the options here.
01:20
So the first one, d squared y over dt squared plus y equals 0.
01:26
This is clearly linear because the constants on the outside, so a0 of t here, is just equal to 1.
01:32
And a1 of t or you could you could call it a2 of t or because it's the second power here is equal to one these are all linear terms okay so this is this is linear looking at the second option we have d squared y over dt squared plus t cubed d squared y oh sorry i've missed i've misread this, this should be d cubed y, d cubed y over dt cubed, plus t cubed, d squared y over dt squared, plus sine of t dy by dt, plus y equals zero...