设f（x）是定义域为R,最小正周期为3π/2的周期函数,当-π/2

题目

设f（x）是定义域为R,最小正周期为3π/2的周期函数,当-π/2<=x<0时,f（x）=cosx；当0<=x<π时,f（x）=sinx,则f（-15π/4）=?

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