What is the particular solution of the differential equation y'+ytanx=sin(2x) where y(0)=1?

cubanwongux

cubanwongux

Answered question

2022-09-09

What is the particular solution of the differential equation y + y tan x = sin ( 2 x ) where y(0)=1?

Answer & Explanation

Azul Lang

Azul Lang

Beginner2022-09-10Added 20 answers

The given equation,
y + y tan ( x ) = sin ( 2 x )
, is of the form:
y + P ( x ) y = Q ( x )
Where P ( x ) = tan ( x ) , and Q ( x ) = sin ( 2 x )
It is known that the integrating factor is:
μ ( x ) = e P ( x ) d x
tan ( x ) d x = log ( sec ( x ) )
μ ( x ) = e log ( sec ( x ) ) = sec ( x )
Multiply the given equation by μ ( x ) :
y sec ( x ) + tan ( x ) sec ( x ) y = sin ( 2 x ) sec ( x )
We know that the left side integrates to μ ( x ) y and we are left with the task of integrating the right side:
sec ( x ) y = sin ( 2 x ) sec ( x ) d x
sec ( x ) y = - 2 cos ( x ) + C
Multiply both side by cos(x)
y = - 2 cos 2 ( x ) + C cos ( x )
Use the boundary condition to find the value of C:
1 = - 2 cos 2 ( 0 ) + C cos ( 0 )
C=3

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