## Thomas' Calculus 13th Edition

$f_t=-sin(2πt-α)\times 2π$ $f_α=sin(2πt-α)$
Take the first partial derivatives of the given function. When taking a partial derivative with respect to t, treat $α$ as a constant, and vice versa: $f_t=-sin(2πt-α)\times 2π$ $f_α=-sin(2πt-α)\times -1=sin(2πt-α)$