已知cos(α-9π/2)=2cos(5π-α),求sin(α-π)^2+3sin(2π-α)cos(5π+α)的值

问题描述:

已知cos(α-9π/2)=2cos(5π-α),求sin(α-π)^2+3sin(2π-α)cos(5π+α)的值

cos(α-9π/2)=cos(a-π/2)=cos(π/2-a)=sina2cos(5π-α)=2cos(π-a)=-2cosasina=-2cosa(sina)^2+(cosa)^2=5(sina)^2/4=1 (sina)^2=4/5 (cosa)^2=1/5sin(α-π)^2+3sin(2π-α)cos(5π+α)=(sina)^2+3(-sina)(-...