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数学
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f(x)=sin(3x+π/4),求f(π/9)的值
第二小问:f(a/3+π/4)=1/2,a∈(π,3π/2),求cos2a
人气:264 ℃ 时间:2020-06-07 18:58:36
解答
f(π/9)=sin(3π+π/4)=sin(π+π/4)=-sinπ/4=-√2/2
f(a/3+π/4)=1/2=cos(π/3)
a/3+π/4=π/3
a/3=π/12
a=π/4
则cos2a=0不应该是f(π/9)=sin(π/3π+π/4)吗??f(π/9)=sin(π/3+π/4)=sin(7π/12)=sin(π-5π/12)=sin5π/12f(a/3+π/4)=1/2=cos(π/3)a/3+π/4=π/3a/3=π/12a=π/4则cos2a=0【?】
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