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问题: 急 三角函数图象

设f(x)是定义域为R,最小正周期为2兀/3的函数,若f(x)=cosx(x大于等于-兀/2,小于0),f(x) =sinx(x大于等于0,小于兀).求f(-15兀/4)的值.

解答:

设f(x)是定义域为R,最小正周期为2π/3的函数,若f(x)=cosx
(-π/2≤x<0),f(x) =sinx(0<x<π).求f(-15π/4)的值.
解:最小正周期为2π/3→
f(-15π/4)=f[(-15π/4)+6*(2π/3)]=
f[(-15π/4)+(12π/3)]=
f[(-45π/12)+(48π/12)]=
f((3π/12)=
f(π/4)=
sin(π/4)=
√2/2