(1)已知sin(π-x)=log以8为底1/4的对数,且x∈(-π/2,0),则cos(π+x)的值?
问题描述：
(1)已知sin(π-x)=log以8为底1/4的对数,且x∈(-π/2,0),则cos(π+x)的值?
答
sin(π-x)
=sinx
=log8(1/4)
=log2³(2)^(-2)
=-(2/3)log2(2)
=-2/3
x∈(-π/2,0)
∴cosx=√5/3
cos(π+x)
=-cosx
=-√5/3