江画工太猩院 ∑ a, cos hxdx+ ∑ b, sin kxdx 2π, f( dx (2)求n f(x)cos node=o cos ndx ∑2 cos kr cos nxx+ bk| sin kr cosnxdx k=1江西理工大学理学院 2 , 20 = ⋅ π a ∫ π = π−π a f (x)dx 1 0 dx a kxdx b kxdx a k k k k cos sin 2 1 1 0 ∫ ∫ ∑ ∫− ∑ ∞ = − ∞ = − = + + π π π π π π (2) . 求an ∫ = ∫π−π π−π nxdx a f x nxdx cos 2 ( )cos 0 [ cos cos sin cos ] 1 ∑ ∫ ∫π−π π−π ∞ = + a kx nxdx + bk kx nxdx k k