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Find the differential equations with the following general solution?please help me I cannot find the solution I have test on this?
y=Ae^-x+Be^-3x where A and B are arbitrary constant
3 Answers
- IndicaLv 74 years ago
This is the solution of an ordinary DE with constant coefficients. (you should know this)
The auxiliary equation of this DE is formed from the e indices viz : (m+1)(m+3)=0
This expands to m²+4m+3=0
The DE is formed by replacing m by dy/dx, m² by d²y/dx², etc
d²y/dx²+4dy/dx+3y = 0
…………………………..
Another way you can do it is to use differentiation to derive 2 additional equations and then eliminate
the arbitrary constants A,B.
y = Ae⁻˟ + Be⁻³˟ … (i)
dy/dx = −Ae⁻˟ − 3Be⁻³˟ … (ii)
d²y/dx² = Ae⁻˟ + 9Be⁻³˟ … (iii)
(ii)+(iii) ⟹ d²y/dx² + dy/dx = 6Be⁻³˟
(i)+(ii) ⟹ y + dy/dx = −2Be⁻³˟
∴ −3(y+dy/dx) = d²y/dx²+dy/dx ⟹ d²ydx²+4dy/dx+3y = 0