Question

The real part of $e^{(3+4i)x}$ is

• A. $e^{3x}$
• B. $\cos 7x$
• C. $e^{3x}\cos 4x$
• D. $e^{3x}\sin 4x$
• E. $0$

Answer 1

Answer: (C)

$z=e^{3x}\cdot e^{4xi}=e^{3x}[\cos 4x+i\sin 4x]$
$Re(z)=e^{3x}\cos 4x$