A finite Fourier series is given by the sum

$\displaystyle f(x) = \sum\limits_{n = 1}^N {{a_n}\sin nx = {a_1}\sin x + {a_2}\sin 2x + ... + {a_N}\sin Nx}

$

Show that the mth coefficient am is given by the formula

$\displaystyle {a_m} = \frac{1}

{\pi }\int_{ - \pi }^\pi {f(x)\sin mxdx}

$

very confused...