00:01
Okay, so here we're looking at we have f of x is equal to e to the power of rx.
00:14
And we're giving the differential equation 2 times the second derivative of y plus the first derivative minus y is equal to 0.
00:32
Basically we set this f of x is equal to y.
00:38
So we need us to find the derivatives first.
00:42
Okay, so since e to the rx is y, the first derivative of that is going to be r times e to the power of rx.
00:56
And then the second derivative is going to equal r squared times e to the power of rx.
01:03
So we're going to plug that in to this equation here.
01:09
So we will get 2 times r squared e to the rx, plus r times e to the rx minus e to the r x is equal to zero.
01:26
So we can factor out the e to the power of rx.
01:31
We will get 2r squared plus r minus 1 is equal to 0.
01:39
I guess we can factor that a little bit further.
01:45
So 2r squared plus r minus 1 will factor 2.
01:50
2r minus 1 times r plus r plus r minus 1 will factor 2.
01:54
1.
01:57
And since that is equal to 0, and e to the rx certainly is going to equal 0, we get that r1 is equal to 1 half, and r2 is equal to negative 1...