# Math Help - Differenation/Differential Equation

1. ## Differenation/Differential Equation

Hi, I'm lost with this question. Never done differential equations before, yet...

From the equation y'' + y' - 2y = x^2, find constants A,B and C such that the function y = Ax2 + Bx + C satisfies the equation.

2. Originally Posted by millerst
Hi, I'm lost with this question. Never done differential equations before, yet...

From the equation y'' + y' - 2y = x^2, find constants A,B and C such that the function y = Ax2 + Bx + C satisfies the equation.
$y = Ax^2 + Bx + C
$

$y' = 2Ax + B$

$y'' = 2A$

$y'' + y' - 2y = x^2$

$2A + (2Ax + B) - 2(Ax^2 + Bx + C) = x^2$

$-2Ax^2 + (2A-2B)x + (2A + B - 2C) = x^2$

match up the coefficients ...

$-2A = 1$

$2A - 2B = 0$

$2A + B - 2C = 0$

solve for A, B, and C.