已知α为锐角,且tanα=1/2,求cos(π/2+α)cos(π-α)/tan(π+α)cos(2π-α).

已知α为锐角,且tanα=1/2,求cos(π/2+α)cos(π-α)/tan(π+α)cos(2π-α).
已知α为锐角,且tanα=1/2,求cos(π/2+α)cos(π-α)/tan(π+α)cos(2π-α).

已知α为锐角,且tanα=1/2,求cos(π/2+α)cos(π-α)/tan(π+α)cos(2π-α).
cos(π/2+α)cos(π-α)/tan(π+α)cos(2π-α）=（-sina）（-cosa）/tana*cosa=cosa
=1/根号（1+tan²a）=2/5*根号5