2nd order non homogenous diff' equation

joeperry

Hi, can someone have a look at thie khanacademy video, go to 5:17 and where is he getting the -4 in the part with (-4-9)/2 from please? thanks.



http://www.youtube.com/watch?v=I3vIAzMcm4Y&feature=autoplay&list=SP96AE8D9C68FEB902&playnext=2

TheBody

joeperry wrote: »

Hi, can someone have a look at thie khanacademy video, go to 5:17 and where is he getting the -4 in the part with (-4-9)/2 from please? thanks.



http://www.youtube.com/watch?v=I3vIAzMcm4Y&feature=autoplay&list=SP96AE8D9C68FEB902&playnext=2

He begins that bit by comparing the constants on both sides of the equal sign. He remarks that:

[latex]2A-3B-4C=0[/latex].

He then subs in the values for A and B that he found already so he gets:

[latex]2(-1)-3(\frac{3}{2})-4C=0[/latex].

Which when multiplied out gives you:

[latex]-2-\frac{9}{2}-4C=0[/latex].

He then combines the [latex]-2[/latex] and the [latex]-\frac{9}{2}[/latex]

(gets a common denominator) to give:

[latex]\frac{-4-9}{2}-4C=0}[/latex]

Simplifing we get:

[latex]\frac{-13}{2}-4C=0}[/latex]

and with a little bit of re-arranging we get that

[latex]C=\frac{-13}{8}}[/latex]

joeperry

Cheers thank you again!!