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Please help solve this question, Im having difficulty with it. Thanks.

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- Mar 13th 2009, 03:03 PMronaldo_07Differential
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Please help solve this question, Im having difficulty with it. Thanks. - Mar 13th 2009, 03:53 PMHallsofIvy
$\displaystyle y_1'= 3y_1+ 4y_2$

$\displaystyle y_2'= -2y_1- y_2$

Differentiate the first equation to get $\displaystyle y_1"= 3y_1'+ 4y_2'$. From the second equation, $\displaystyle y_1"= 3y_1'+ 4(-2y_1- y_2)= 2y_1'- 8y_1- 4y_2$.

From the first equation again, $\displaystyle 4y_2= y_1'- 3y_1$ so $\displaystyle y_1"= 3y_1'- 8y_1- (y_1'- 3y_1)= 2y_1'- 5y_1$.

That is, $\displaystyle y_1"- 2y_1'+ 5y_1= 0$. Can you solve that?

That will have, of course, two constants in the general solution. To find $\displaystyle y_2$, use $\displaystyle 4y_2= y_1'- 3y_1$ so as not to introduce more constants. - Mar 14th 2009, 11:04 AMronaldo_07
I got $\displaystyle y=Ae^{(landa-2)x}+Be^{(landa+2)x}$ is this correct?