1.

Form a differential equation representing the given family of curves by eliminating arbitrary constant a and b.y = e^x(acosx + bsinx)

Answer»

y = ex(a cos x + b sin x) ….(1) 

differentiate w.r.t x 

y1 = ex(a cosx + b sinx) + ex(-a sin x + b cos x) ….(2) 

putting (1) in (2); we get 

⇒ y1 = y + ex(b cos x – a sin x) 

⇒ y1 – y = ex(b cos x – a sinx) ….(3) 

again differentiating w.r.t x, we get 

⇒ y2 – y1 = ex (b cos x – a sin x) + ex (-b sin x – a cos x) ….(4) 

putting (3) and (1) in (4), we get 

⇒ y2 – y1= (y1 – y) +(-y) 

⇒ y2 – 2y1+ 2y = 0 is the required differential equation.



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