4.
: , , , .. .
f (x), , , , , , ≠0, :
f (x + T) = f (x).
f (x), ҷ .
.
, . = 2π = sin , = cos ..
1. , , .
2. f (x) , f (a x) , ≠0, = const.
, y = sin x, y = cos x =2π, y = sin kx y = cos kx . y = sin kx = cos kx .
3. , , , .. f (x) = f (x + T), o .
( 2).
2
, .
f (x) φ() [ , b ], ,
.
, f (x)= [0, l]. [0;1]. :
.
, f (x) = x [0,l].
f,(x), f 2 (x),, fn (x) [ a, b ], , ..
{1, cos x, sin x, cos2 x, sin2 x,..., cos nx, sin nx,... }, ÎZ, [-π, π], .. , .