y"+y'=6x+18-x^2
Характеристическое уравнение однородного:
Частное решение ищем в виде :
Тогда общее решение
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y"+y'=6x+18-x^2
Характеристическое уравнение однородного:![\lambda^2+\lambda=0=>\lambda=0\:\:\:\:\lambda=-1=>x_o=C_1e^{-x}+C_2 \lambda^2+\lambda=0=>\lambda=0\:\:\:\:\lambda=-1=>x_o=C_1e^{-x}+C_2](https://tex.z-dn.net/?f=%5Clambda%5E2%2B%5Clambda%3D0%3D%3E%5Clambda%3D0%5C%3A%5C%3A%5C%3A%5C%3A%5Clambda%3D-1%3D%3Ex_o%3DC_1e%5E%7B-x%7D%2BC_2)
Частное решение ищем в виде
: ![6Ax+2B+3Ax^2+2Bx+C=6x+18-x^2\\ (3A+1)x^2+(6A+2B-6)x+(2B+C-18)=0\\ 3A+1=0=>A=\dfrac{-1}{3}\\ 6A+2B-6=0=>-2+2B-6=0=>B=4\\ 2B+C-18=0=>8+C-18=0=>C=10\\ x_r=\dfrac{-1}{3}x^3+4x^2+10x 6Ax+2B+3Ax^2+2Bx+C=6x+18-x^2\\ (3A+1)x^2+(6A+2B-6)x+(2B+C-18)=0\\ 3A+1=0=>A=\dfrac{-1}{3}\\ 6A+2B-6=0=>-2+2B-6=0=>B=4\\ 2B+C-18=0=>8+C-18=0=>C=10\\ x_r=\dfrac{-1}{3}x^3+4x^2+10x](https://tex.z-dn.net/?f=6Ax%2B2B%2B3Ax%5E2%2B2Bx%2BC%3D6x%2B18-x%5E2%5C%5C%20%283A%2B1%29x%5E2%2B%286A%2B2B-6%29x%2B%282B%2BC-18%29%3D0%5C%5C%203A%2B1%3D0%3D%3EA%3D%5Cdfrac%7B-1%7D%7B3%7D%5C%5C%206A%2B2B-6%3D0%3D%3E-2%2B2B-6%3D0%3D%3EB%3D4%5C%5C%202B%2BC-18%3D0%3D%3E8%2BC-18%3D0%3D%3EC%3D10%5C%5C%20x_r%3D%5Cdfrac%7B-1%7D%7B3%7Dx%5E3%2B4x%5E2%2B10x)
Тогда общее решение![x=x_o+x_r=C_1e^{-x}+C_2-\dfrac{1}{3}x^3+4x^2+10x x=x_o+x_r=C_1e^{-x}+C_2-\dfrac{1}{3}x^3+4x^2+10x](https://tex.z-dn.net/?f=x%3Dx_o%2Bx_r%3DC_1e%5E%7B-x%7D%2BC_2-%5Cdfrac%7B1%7D%7B3%7Dx%5E3%2B4x%5E2%2B10x)