I have the following equation to calculate its derivative:
$f(x) = e^{3x}(\sin(x)+\cos(x))$
I used the product rule and I got this answer:
$e^{3x}(\sin(x)+\cos(x))+e^{3x}(\cos(x)-\sin(x))$
But the answer at the end of the book is:
$3e^{3x}(\sin(x)+\cos(x))+e^{3x}(\cos(x)-\sin(x))$
I am scratching my head to find where that $3$ came from. I think I have to use chain rule here as well, but I am not sure to take which part of equation as $z$.