[math-fun] for the fun

k*Pi/2=-(sum(((-sqrt(-4*cos((c+a)*x)*cos((d+b)*x)+cos((d+a)*x)^2+2*cos((c+b)*x)*cos((d+a)*x)+cos((c+b)*x)^2)+cos((d+a)*x)+cos((c+b)*x))^n*(sin((d-c)*n*x)+sin((b-a)*n*x)))/(n*2^n*cos((d+b)*x)^n),n=1..infinity))+(c+a)*x; k in Z a,b,c,d in R when sqrt(delta) exist in R