Expression 4: cosine left parenthesis, StartFraction, "s" pi "x" Over 2 "r" , EndFraction , right parenthesis cosine left parenthesis, StartFraction, "s" pi "y" Over 2 "r" , EndFraction , right parenthesis equals left bracket, cos left parenthesis, StartFraction, "s" pi Over 2 , EndFraction , right parenthesis , right bracket Superscript, "p" , Baseline Has graph.cossπx2rcossπy2r=cossπ2p