hello, i'm a self learner currently learning fourier series. Anyway, I'm having some problem with a question regarding the inner product of two complex functions. This is defined by an integral from negative infi to positive infi of the multiplication of one function and the complex conjugate of the other. Since it is an integral of two function i'm wondering if integration by parts that we learn in high school which applies for real function is workable on complex functions? A link to a proof will be even more appreciated! Thank!