Write SQL query to solve given problem: Which item provided for projects with Mathematics as a primary subject is the most expensive?. Keep the solution inside sql tag ```sql [SQL-Query] ```
SELECT T1.item_name FROM resources AS T1 INNER JOIN projects AS T2 ON T1.projectid = T2.projectid WHERE T2.primary_focus_subject = 'Mathematics' ORDER BY T1.item_unit_price DESC LIMIT 1