Terms containing expansion of a function in a series

Subject	English	Russian
math.	a Fourier series is an expansion of a function in a series of sines and cosines	ряд по синусам и косинусам
math.	expansion of a function in a series	разложение функции в ряд
math.	the a power series expansion of a function in x	разложение в ряд по степеням