Literal a)

f1=figure;

syms k n x

s=symsum((((-1)^k-1)/((k^2)*pi))*cos(k*pi)+((1-2*(-1)^k)/k)*sin(x*k),1,10000);

k=linspace(-10,10,1000);

y=-(pi/4)+(1./2.*(20002.*cos(k.*pi).*(-1).^k.*cos(k)-20002.*cos(k.*pi).*(-1).^k-20002.*cos(k.*pi).*cos(k)+20002.*cos(k.*pi)-k.*pi.*sin(10001.*k).*cos(k)+sin(10001.*k).*k.*pi+2.*k.*pi.*(-1).^k.*sin(10001.*k).*cos(k)-2.*sin(10001.*k).*k.*pi.*(-1).^k+k.*pi.*cos(10001.*k).*sin(k)-2.*k.*pi.*(-1).^k.*cos(10001.*k).*sin(k))./k.^2./pi./(cos(k)-1)-1./2.*(2.*cos(k.*pi).*(-1).^k.*cos(k)-2.*cos(k.*pi).*(-1).^k-2.*cos(k.*pi).*cos(k)+2.*cos(k.*pi)+sin(k).*k.*pi-2.*sin(k).*k.*pi.*(-1).^k)./k.^2./pi./(cos(k)-1))+ eps;

plot(k,y)

grid

Literal b)

f1=figure;

syms k n x

s=symsum((1/k^2)*(1-cos(k*pi/2))*(cos(k*pi*x/2)),1,10000)

k=linspace(-2,2,80);

y=(-1/4)+(4./pi.^2).*(1./2./k.^2.*(cos(1./2.*k.*pi)-1).*cos(10001./2.*k.*pi)+1./2./k.^2.*sin(10001./2.*k.*pi).*sin(1./2.*k.*pi)-1./2./k.^2.*(cos(1./2.*k.*pi)-1).*cos(1./2.*k.*pi)-1./2./k.^2.*sin(1./2.*k.*pi).^2)+ eps;

plot(k,y)

grid