若(sinα+cosα)/(sinα-cosα)=2,求sin(α-5π)sin(3π/2-α)的值

问题描述:

若(sinα+cosα)/(sinα-cosα)=2,求sin(α-5π)sin(3π/2-α)的值

∵(sinα+cosα)/(sinα-cosα)=2==>sinα+cosα=2(sinα-cosα)==>sinα=3cosα==>(3cosα)^2+(cosα)^2=1==>10(cosα)^2=1∴(cosα)^2=1/10故sin(α-5π)sin(3π/2-α)=-sinα(-cosα)=sinαcosα=(3cosα)cosα=3...