integral of cos(ax)e^{bx}

Lösung

\int cos (a x) e^{b x} d x

\frac{a e ^{b x} sin ( a x )}{a ^{2} + b ^{2}} + \frac{b e ^{b x} cos ( a x )}{a ^{2} + b ^{2}} + C

Schritte zur Lösung

\int cos (a x) e^{b x} d x

Wende die partielle Integration an

= e^{b x} \frac{1}{a} sin (a x) - \int e^{b x} b \frac{1}{a} sin (a x) d x

Entferne die Konstante:

\int a \cdot f (x) d x = a \cdot \int f (x) d x

= e^{b x} \frac{1}{a} sin (a x) - b \frac{1}{a} \cdot \int e^{b x} sin (a x) d x

Vereinfache

b \frac{1}{a} : \frac{b}{a}

= e^{b x} \frac{1}{a} sin (a x) - \frac{b}{a} \cdot \int e^{b x} sin (a x) d x

Wende die partielle Integration an

= e^{b x} \frac{1}{a} sin (a x) - \frac{b}{a} (- e^{b x} \frac{1}{a} cos (a x) - \int - b e^{b x} \frac{1}{a} cos (a x) d x)

Entferne die Konstante:

\int a \cdot f (x) d x = a \cdot \int f (x) d x

= e^{b x} \frac{1}{a} sin (a x) - \frac{b}{a} (- e^{b x} \frac{1}{a} cos (a x) - (- b \frac{1}{a} \cdot \int e^{b x} cos (a x) d x))

Vereinfache

- b \frac{1}{a} : - \frac{b}{a}

= e^{b x} \frac{1}{a} sin (a x) - \frac{b}{a} (- e^{b x} \frac{1}{a} cos (a x) - (- \frac{b}{a} \cdot \int e^{b x} cos (a x) d x))

Deshalb

\int e^{b x} cos (a x) d x = e^{b x} \frac{1}{a} sin (a x) - \frac{b}{a} (- e^{b x} \frac{1}{a} cos (a x) - (- \frac{b}{a} \cdot \int e^{b x} cos (a x) d x))

Isoliere

\int e^{b x} cos (a x) d x

= \frac{a e ^{b x} sin ( a x )}{a ^{2} + b ^{2}} + \frac{b e ^{b x} cos ( a x )}{a ^{2} + b ^{2}}

Füge eine Konstante zur Lösung hinzu

= \frac{a e ^{b x} sin ( a x )}{a ^{2} + b ^{2}} + \frac{b e ^{b x} cos ( a x )}{a ^{2} + b ^{2}} + C

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