To Find Nth Derivative of e2x sin3x sin2x
In this tutorial, we learn how to find the nth derivative of expressions involving eax · sin(bx) · sin(cx) using identities and standard nth derivative formulas.
Solution
Let
u = e2x
v = sin3x · sin2x
u = e2x
v = sin3x · sin2x
Using Trigonometric Identity
sinA · sinB = ½ [ cos(A − B) − cos(A + B) ]
A = 3x
B = 2x
∴ A − B = x
∴ A + B = 5x
B = 2x
∴ A − B = x
∴ A + B = 5x
Rewrite the Function
y = e2x · ½ [ cos x − cos 5x ]
= ½ [ e2x cos x − e2x cos 5x ]
= ½ [ e2x cos x − e2x cos 5x ]
Standard Formula
If y = eAx cos(Bx + C), then
dny/dxn = (A² + B²)n/2 eAx cos(Bx + C + n tan−1(B/A))
dny/dxn = (A² + B²)n/2 eAx cos(Bx + C + n tan−1(B/A))
Nth Derivative of e2x cos x
= ½ · 5n/2 e2x cos(x + n tan−1(1/2))
Nth Derivative of e2x cos 5x
= ½ · 29n/2 e2x cos(5x + n tan−1(5/2))
Final Answer
½ · 5n/2 e2x cos(x + n tan−1(1/2))
−
½ · 29n/2 e2x cos(5x + n tan−1(5/2))
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