表达式4: left parenthesis, cos left parenthesis, "n" "b" "t" , right parenthesis cos left parenthesis, "b" "t" , right parenthesis , cos left parenthesis, "n" "b" "t" , right parenthesis sin left parenthesis, "b" "t" , right parenthesis , right parenthesiscosnbtcosbt,cosnbtsinbt
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定义域t最小值:
less than or equal to "t" less than or equal to≤t≤