Expression 9: polygon left parenthesis, negative 0.5csc left parenthesis, "a" Subscript, 6 , Baseline , right parenthesis left parenthesis, sin left parenthesis, "a" Subscript, 5 , Baseline , right parenthesis , cos left parenthesis, "a" Subscript, 5 , Baseline , right parenthesis minus cos left parenthesis, "a" Subscript, 6 , Baseline , right parenthesis , right parenthesis left brace, 1 less than "a" Subscript, 4 , Baseline , right brace , right parenthesispolygon−0.5csca6sina5,cosa5−cosa61<a4