cos(arctan(-1)) means cosalpha of an angle alpha, where tanalpha=-1. tanalpha=-1 for alpha=(3pi)/4 or alpha=(-pi)/4.
cos((3pi)/4)=-1/sqrt2 and cos((-pi)/4)=1/sqrt2. Hence cos(arc tan(-1))=+-1/sqrt2
sin(arc csc(-1)) means sinbeta of an angle beta, where cscbeta=-1.
cscbeta=-1 for beta=(3pi)/2 and sin((3pi)/2)=-1. Hence sin(arc csc(-1))=-1
Hence, cos(arctan(-1))+sin(arc csc(-1))=-1+-1/sqrt2