高一数学在线若cos(α
若c(α-3/2π）=1/5求f(a)的值
(1)f(a)=[sin(α-π/2)cos(3π/2+α)tan(π-α)]/[tan(-α-π)sin(-π-α)] =[(-cosα)(sinα)(-tanα)]/[(-tanα)(sinα)] =-cosα (2)由cos(α-3π/2)=1/5 得-sinα=1/5 即sinα=-1/5 又α是第三象限角 所以cosα=-(2/5)√6 所以f(α)=-cosα=(2/5)√6