cos(arctan(-1))cos(arctan(−1)) means cosalphacosα of an angle alphaα, where tanalpha=-1tanα=−1. tanalpha=-1tanα=−1 for alpha=(3pi)/4α=3π4 or alpha=(-pi)/4α=−π4.
cos((3pi)/4)=-1/sqrt2cos(3π4)=−1√2 and cos((-pi)/4)=1/sqrt2cos(−π4)=1√2. Hence cos(arc tan(-1))=+-1/sqrt2cos(arctan(−1))=±1√2
sin(arc csc(-1))sin(arccsc(−1)) means sinbetasinβ of an angle betaβ, where cscbeta=-1cscβ=−1.
cscbeta=-1cscβ=−1 for beta=(3pi)/2β=3π2 and sin((3pi)/2)=-1sin(3π2)=−1. Hence sin(arc csc(-1))=-1sin(arccsc(−1))=−1
Hence, cos(arctan(-1))+sin(arc csc(-1))=-1+-1/sqrt2cos(arctan(−1))+sin(arccsc(−1))=−1±1√2