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确定下列三角函数值的正负号:(1):sin(一17兀/5)(2):cos21兀/8)(3)tan19兀/5)
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确定下列三角函数值的正负号:(1):sin(一17兀/5) (2):cos21兀/8) (3)
tan19兀/5)
tan19兀/5)
▼优质解答
答案和解析
解sin(一17兀/5)
=-sin(17π/5)
=-sin(4π-3π/5)
=-sin(-3π/5)
=sin(3π/5)
>0
即sin(一17兀/5) 是正号
cos(21兀/8)
=cos(2π+5π/8)
=cos(5π/8)
<0
故cos(21兀/8)的值是负号
tan(19π/5)
=tan(3π+4π/5)
=tan(4π/5)
=-tanπ/5
<0
故tan(19π/5)是负号.
=-sin(17π/5)
=-sin(4π-3π/5)
=-sin(-3π/5)
=sin(3π/5)
>0
即sin(一17兀/5) 是正号
cos(21兀/8)
=cos(2π+5π/8)
=cos(5π/8)
<0
故cos(21兀/8)的值是负号
tan(19π/5)
=tan(3π+4π/5)
=tan(4π/5)
=-tanπ/5
<0
故tan(19π/5)是负号.
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